Crash if some auth parameters are empty

[BishopGIS]

uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #05 pc 00d85264  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #06 pc 00d81c69  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #07 pc 00d8119e  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #08 pc 00d810f3  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so (__cxa_throw+115)
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #09 pc 0034815d  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so (ngs::Options::operator[](std::__ndk1::basic_string<char, std::__ndk1::char_traits<char>, std::__ndk1::allocator<char>>) const+317)
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #10 pc 0034a674  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so (ngs::AuthStore::authAdd(std::__ndk1::basic_string<char, std::__ndk1::char_traits<char>, std::__ndk1::allocator<char>> const&, ngs::Options const&)+132)
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #11 pc 0028374b  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so (ngsURLAuthAdd(char const*, char**)+235)
2019-08-08 11:27:03.989 7799-7799/? A/DEBUG:     #12 pc 00296199  /data/app/com.nextgis.nextgismobile-uzlCXPmAO5Kbdzr4kKQAow==/lib/x86/libngstore.so (Java_com_nextgis_maplib_API_URLAuthAdd+249)