Retry data-URI parsing failure after removing whitespace

Though not valid per the spec to include whitespace in the non-data portion of the data-URI, browser do perform a similar operation. The whitespace removal is done after initial failure in order to minimize impact on documents with a correcty formatted data-URIs.

fixes dompdf#1386

Author: bsweeney

src/Helpers.php

@@ -287,8 +287,13 @@ public static function is_percent($value): bool
      */
     public static function parse_data_uri($data_uri)
     {
-        if (!preg_match('/^data:(?P<mime>[a-z0-9\/+-.]+)(;charset=(?P<charset>[a-z0-9-])+)?(?P<base64>;base64)?\,(?P<data>.*)?/is', $data_uri, $match)) {
-            return false;
+        $expression = '/^data:(?P<mime>[a-z0-9\/+-.]+)(;charset=(?P<charset>[a-z0-9-])+)?(?P<base64>;base64)?\,(?P<data>.*)?/is';
+        if (!preg_match($expression, $data_uri, $match)) {
+            $parts = explode(",", $data_uri);
+            $parts[0] = preg_replace('/\\s/', '', $parts[0]);
+            if (preg_match('/\\s/', $data_uri) && !preg_match($expression, implode(",", $parts), $match)) {
+                return false;
+            }
         }
 
         $match['data'] = rawurldecode($match['data']);