Issue #2835062 by OnkelTem: XML plugin breaks on first empty source (urls)

src/DataParserPluginBase.php

@@ -110,8 +110,11 @@ abstract class DataParserPluginBase extends PluginBase implements DataParserPlug
     $this->fetchNextRow();
     // If there was no valid row there, try the next url (if any).
     if (is_null($this->currentItem)) {
-      if ($this->nextSource()) {
+      while ($this->nextSource()) {
         $this->fetchNextRow();
+        if ($this->valid()) {
+          break;
+        }
       }
     }
     if ($this->valid()) {