strings: negative Repeat count

[bang9211]

When I tried to run the below code, panic is occured

package main

import "github.com/go-xmlfmt/xmlfmt"

func main() {
	msg := `<!-- 무조건 착신전환 조회 -->
	<?xml version="1.0" encoding="utf-8"?>
	<message name="DIS_USER_SSVC" tid="1591918441">
	  <!-- 결과 코드 : 0(성공) / 그 외(실패) -->
	  <Result>0</Result>
	  <parameter>
		<SsvcList>
		  <!-- 가입/사용 여부 : 3(가입+사용 중) / 2(가입+미사용) -->
		  <CFU>2</CFU>
		  <!-- 착신 번호(CFU 가 3인 경우 사용) -->
		  <!-- <DATA>0261216281</DATA> -->
		</SsvcList>
	  </parameter>
	</message>`
	xmlfmt.FormatXML(string(msg), "", "\t")
}

the error trace is

panic: strings: negative Repeat count

goroutine 1 [running]:
strings.Repeat({0x102cb4c14, 0x1}, 0xffffffffffffffff)
        /usr/local/go/src/strings/strings.go:529 +0x41c
github.com/go-xmlfmt/xmlfmt.replaceTag.func1({0x1400011e195, 0xa})
        /Users/hanyoungtak/Documents/go/pkg/mod/github.com/go-xmlfmt/xmlfmt@v0.0.0-20191208150333-d5b6f63a941b/xmlfmt.go:48 +0x24c
regexp.(*Regexp).ReplaceAllStringFunc.func1({0x1400011c300, 0x1cd, 0x300}, {0x14000016240, 0x2, 0x2})
        /usr/local/go/src/regexp/regexp.go:596 +0x78
regexp.(*Regexp).replaceAll(0x1400007c0a0, {0x0, 0x0, 0x0}, {0x1400011e000, 0x19f}, 0x2, 0x14000105e98)
        /usr/local/go/src/regexp/regexp.go:634 +0x314
regexp.(*Regexp).ReplaceAllStringFunc(0x1400007c0a0, {0x1400011e000, 0x19f}, 0x14000068210)
        /usr/local/go/src/regexp/regexp.go:595 +0x74
github.com/go-xmlfmt/xmlfmt.FormatXML({0x102cbacae, 0x1cf}, {0x0, 0x0}, {0x102cb4c14, 0x1})
        /Users/hanyoungtak/Documents/go/pkg/mod/github.com/go-xmlfmt/xmlfmt@v0.0.0-20191208150333-d5b6f63a941b/xmlfmt.go:25 +0xc4
main.main()
        /Users/hanyoungtak/Documents/go/src/xml-test/main.go:20 +0x4c

[AntonioSun]

fixed. see #2