[CRT] Add parameter check to _mbscmp

Fixes crash in msvcrt_winetest::string

sdk/lib/crt/mbstring/mbscmp.c

@@ -1,10 +1,14 @@
 #include <mbstring.h>
 #include <string.h>
+#include <precomp.h>
 
 /*
  * @implemented
  */
 int _mbscmp(const unsigned char *str1, const unsigned char *str2)
 {
+    if (!MSVCRT_CHECK_PMT(str1 && str2))
+        return _NLSCMPERROR;
+
   return strcmp((const char*)str1, (char*)str2);
 }