leave enough space for the trailing NUL when converting UTF-16 to UTF-32 in Mac conversion

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38603 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/strconv.cpp

@@ -2760,7 +2760,7 @@ public:
     {
         OSStatus status = noErr ;
         ByteCount byteOutLen ;
-        ByteCount byteInLen = strlen(psz) ;
+        ByteCount byteInLen = strlen(psz) + 1;
         wchar_t *tbuf = NULL ;
         UniChar* ubuf = NULL ;
         size_t res = 0 ;