Fix compatibility issue with php 7.2 (#129)

Author: ddeath

src/Rebing/GraphQL/GraphQLController.php

@@ -14,7 +14,7 @@ public function query(Request $request, $schema = null)
 
         // If there are multiple route params we can expect that there
         // will be a schema name that has to be built
-        if (count($request->route()->parameters) > 1) {
+        if ($request->route()->parameters && count($request->route()->parameters) > 1) {
             $schema = implode('/', $request->route()->parameters);
         }