Issue #3406547 by robphillips: Fixes dialogOptions when using GET Ajax requests.

src/Render/MainContent/Bootstrap4ModalRenderer.php

@@ -37,7 +37,12 @@ class Bootstrap4ModalRenderer extends DialogRenderer {
 
     // Determine the title: use the title provided by the main content if any,
     // otherwise get it from the routing information.
+    if ($request->getMethod() === 'GET') {
+      $options = $request->query->all()['dialogOptions'] ?? [];
+    }
+    else {
       $options = $request->request->all()['dialogOptions'] ?? [];
+    }
 
     $response->addCommand(new OpenBootstrap4ModalDialogCommand($title, $content, $options));
     return $response;