Fix an out-of-boundary issue for wide string

core/include/fxcrt/fx_string.h

Index: core/include/fxcrt/fx_string.h
diff --git a/core/include/fxcrt/fx_string.h b/core/include/fxcrt/fx_string.h
index fe56e1867ecaf73110c162ca4810a129b74d4bb6..26b04b70fad6f12c70e7ccf4dd7b9601d8c4872a 100644
--- a/core/include/fxcrt/fx_string.h
+++ b/core/include/fxcrt/fx_string.h
@@ -634,9 +634,11 @@ public:
 
     static CFX_WideString	FromLocal(const char* str, FX_STRSIZE len = -1);
 
-    static CFX_WideString	FromUTF8(const char* str, FX_STRSIZE len = -1);
+    static CFX_WideString	FromUTF8(const char* str, FX_STRSIZE len);
 
-    static CFX_WideString	FromUTF16LE(const unsigned short* str, FX_STRSIZE len = -1);
+    static CFX_WideString	FromUTF16LE(const unsigned short* str, FX_STRSIZE len);
+
+    static FX_STRSIZE       WStringLength(const unsigned short* str);
 
     operator FX_LPCWSTR() const
     {