kernel32: Handle NULL locale name in IsValidLocaleName().

dlls/kernel32/locale.c

@@ -2656,6 +2656,9 @@ BOOL WINAPI IsValidLocaleName( LPCWSTR locale )
 {
     struct locale_name locale_name;
 
+    if (!locale)
+        return FALSE;
+
     /* string parsing */
     parse_locale_name( locale, &locale_name );
 

dlls/kernel32/tests/locale.c

@@ -4179,6 +4179,8 @@ static void test_IsValidLocaleName(void)
     ok(!ret, "IsValidLocaleName should have failed\n");
     ret = pIsValidLocaleName(LOCALE_NAME_INVARIANT);
     ok(ret, "IsValidLocaleName failed\n");
+    ret = pIsValidLocaleName(NULL);
+    ok(!ret, "IsValidLocaleName should have failed\n");
 }
 
 static void test_CompareStringOrdinal(void)