Responding to pull request review feedback

- messages.getQuoteObjectUrl: early return
- backup.js: explaining variables for long if statement
- types/messages.js: Log if thumbnail has neither data nor path
- sendmessage.js:
  - remove extraneous logging
  - fix indentation
  - upload attachments and thumbnails in parallel
- preload: don't load fs for tests, just fse
- _conversation.scss: split two selectors into two lines, 0px -> 0
- backup_test.js: use fse.existsSync and comment twoSlashes regex
- network_tests_view_test.js: Comment duplicate assignment to window.getSocketStatus

js/modules/types/message.js

@@ -274,6 +274,13 @@ exports.createAttachmentDataWriter = (writeExistingAttachmentData) => {
 
       // we want to be bulletproof to thumbnails without data
       if (!data || !path) {
+        console.log(
+          'Thumbnail had neither data nor path.',
+          'id:',
+          message.id,
+          'source:',
+          message.source
+        );
         return thumbnail;
       }