[fix] : Fix undefined variable $2

Author: Hayao0819

lib/parsearg.sh

@@ -49,7 +49,7 @@ parsearg(){
     local _args=("$@") _noarg=()
     local _current="" _arg="" _var="" _setarg=false
     while [[ -n "${1-""}" ]]; do
-        _current="$1" _arg="$2" _var="" _setarg=false
+        _current="$1" _arg="${2-""}" _var="" _setarg=false
 
         if [[ "$_current" = "--" ]]; then
             shift 1