Improve sanitization of color inputs

MD_STD_IN.php

@@ -98,7 +98,9 @@ public static function sanitize_rgb_color($input):string {
             FILTER_SANITIZE_STRING,
             FILTER_FLAG_NO_ENCODE_QUOTES);
 
-        if (!(preg_match('/^[a-zA-Z0-9]{3}$/', $output)) && !(preg_match('/^[a-zA-Z0-9]{6}$/', $output))) {
+        if ($output === false
+            || ((preg_match('/^[a-zA-Z0-9]{3}$/', $output)) === false && (preg_match('/^[a-zA-Z0-9]{6}$/', $output)) === false)
+        ) {
             throw new MDInvalidColorCode("Invalid color code provided: " . $output);
         }