program crash when test hotwords in andriod and ios

**error log for andriod:**
`2023-08-31 17:10:05.242 23487-24241 libc                    com.k2fsa.sherpa.ncnn                A  Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x20 in tid 24241 (Thread-7), pid 23487 (fsa.sherpa.ncnn)
2023-08-31 17:10:05.472 24258-24258 DEBUG                   pid-24258                            A  pid: 23487, tid: 24241, name: Thread-7  >>> com.k2fsa.sherpa.ncnn <<<
2023-08-31 17:10:05.724 24258-24258 DEBUG                   pid-24258                            A        #00 pc 0000000000021054  /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/lib/arm64/libsherpa-ncnn-core.so (sherpa_ncnn::ContextGraph::ForwardOneStep(sherpa_ncnn::ContextState const*, int) const+12) (BuildId: b21b666f6a77aa6a0ee5427e1e3e3d737da77c12)
2023-08-31 17:10:05.724 24258-24258 DEBUG                   pid-24258                            A        #01 pc 000000000003a470  /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/lib/arm64/libsherpa-ncnn-core.so (sherpa_ncnn::ModifiedBeamSearchDecoder::Decode(ncnn::Mat, sherpa_ncnn::Stream*, sherpa_ncnn::DecoderResult*)+2824) (BuildId: b21b666f6a77aa6a0ee5427e1e3e3d737da77c12)
2023-08-31 17:10:05.724 24258-24258 DEBUG                   pid-24258                            A        #02 pc 000000000003c820  /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/lib/arm64/libsherpa-ncnn-core.so (sherpa_ncnn::Recognizer::Impl::DecodeStream(sherpa_ncnn::Stream*) const+580) (BuildId: b21b666f6a77aa6a0ee5427e1e3e3d737da77c12)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #10 pc 00000000000038fc  [anon:dalvik-classes3.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk!classes3.dex] (com.k2fsa.sherpa.ncnn.SherpaNcnn.decode+4)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #14 pc 00000000020118a0  /memfd:/jit-cache (deleted) (com.k2fsa.sherpa.ncnn.MainActivity.readPcmFromAssets+640)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #19 pc 00000000000027c6  [anon:dalvik-classes3.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk!classes3.dex] (com.k2fsa.sherpa.ncnn.MainActivity.readPcmFromAssets+86)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #22 pc 0000000000001f4c  [anon:dalvik-classes3.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk!classes3.dex] (com.k2fsa.sherpa.ncnn.MainActivity.access$readPcmFromAssets)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #25 pc 0000000000001d9c  [anon:dalvik-classes3.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk!classes3.dex] (com.k2fsa.sherpa.ncnn.MainActivity$onclick$1.invoke+8)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #28 pc 0000000000001d58  [anon:dalvik-classes3.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk!classes3.dex] (com.k2fsa.sherpa.ncnn.MainActivity$onclick$1.invoke)
2023-08-31 17:10:05.725 24258-24258 DEBUG                   pid-24258                            A        #31 pc 00000000003a3658  [anon:dalvik-classes.dex extracted in memory from /data/app/com.k2fsa.sherpa.ncnn-TBEcWxQLxvHnK1PaOKfmPQ==/base.apk] (kotlin.concurrent.ThreadsKt$thread$thread$1.run+4)
---------------------------- PROCESS ENDED (23487) for package com.k2fsa.sherpa.ncnn ----------------------------`

btw, the function AAssetManager_open https://github.com/k2-fsa/sherpa-ncnn/blob/401de811948a3435604b0bc0505b577d595eda96/sherpa-ncnn/csrc/recognizer.cc#L246C4-L246C75, can only read hotwords file in apk, not in storage. apk has to update if hotwords file is changed. it is too heavy.

Please pass null for the following function to assetManager.

sherpa-ncnn/android/SherpaNcnn/app/src/main/java/com/k2fsa/sherpa/ncnn/SherpaNcnn.kt

Line 42 in 401de81

assetManager: AssetManager? = null,

please see

sherpa-ncnn/android/SherpaNcnn/app/src/main/java/com/k2fsa/sherpa/ncnn/SherpaNcnn.kt

Lines 47 to 51 in 401de81

    
           if (assetManager != null) { 
        
               ptr = newFromAsset(assetManager, config) 
        
           } else { 
        
               ptr = newFromFile(config) 
        
           }

Thanks, v2.1.1 fixes this crash issue, it works well for andriod and ios. And AAssetManager_open, just ignore it, my bad misunderstanding.

	if (assetManager != null) {
	ptr = newFromAsset(assetManager, config)
	} else {
	ptr = newFromFile(config)
	}