LibWeb: Transform errant return to a break in form submission

There are more steps to be run after extracting the form body and type.

Userland/Libraries/LibWeb/HTML/HTMLFormElement.cpp

@@ -775,7 +775,7 @@ ErrorOr<void> HTMLFormElement::submit_as_entity_body(URL::URL parsed_action, Vec
         // 2. Let mimeType be the isomorphic encoding of the concatenation of "multipart/form-data; boundary=" and the multipart/form-data
         //    boundary string generated by the multipart/form-data encoding algorithm.
         mime_type = POSTResource::RequestContentType::MultipartFormData;
-        return {};
+        break;
     }
     case EncodingTypeAttributeState::PlainText: {
         // -> text/plain