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/models/messages.js

@@ -214,11 +214,11 @@
     },
     getQuoteObjectUrl() {
       const thumbnail = this.quoteThumbnail;
-      if (thumbnail && thumbnail.objectUrl) {
-        return thumbnail.objectUrl;
+      if (!thumbnail || !thumbnail.objectUrl) {
+        return null;
       }
 
-      return null;
+      return thumbnail.objectUrl;
     },
     getQuoteContact() {
       const quote = this.get('quote');