Fix String::create(_, 0) without HX_SMART_STRINGS

When smart strings are enabled, this always returns an empty string,
however, if they are disabled this currently has different behaviour
depending on the type of character passed in.

This fixes the behaviour so that it also returns an empty string for
wchar_t and char16_t strings when smart strings are disabled.

Author: tobil4sk

src/String.cpp

@@ -454,6 +454,9 @@ inline String TCopyString(const T *inString,int inLength)
       }
       else
       {
+         if (inLength == 0) {
+            return String::emptyString;
+         }
          int length = inLength > 0 ? inLength : 0;
          const char *ptr = TConvertToUTF8(inString, &length, 0, true );
          return String(ptr,length);