PHP7.2 fix (#2848)

functions/mime.php

@@ -1397,8 +1397,8 @@ function sq_casenormalize(&$val){
 function sq_skipspace($body, $offset){
     $me = 'sq_skipspace';
     preg_match('/^(\s*)/s', substr($body, $offset), $matches);
-    if (sizeof($matches{1})){
-        $count = strlen($matches{1});
+    if (!empty($matches[1])){
+        $count = strlen($matches[1]);
         $offset += $count;
     }
     return $offset;