The paste handler (boot.js) bailed entirely when the clipboard contained
both text and image items, preventing image attachment in the most common
real-world scenario: right-click → Copy Image from browsers, Notes, Slack,
etc. — these almost always carry a text/html or text/plain representation
alongside the image.
Previous behavior (from #1620 fix):
- clipboard has text only → normal text paste (correct)
- clipboard has image only → attach image (correct)
- clipboard has BOTH → text pasted, image silently dropped (wrong)
New behavior:
- clipboard has text only → normal text paste (unchanged)
- clipboard has image only → preventDefault + attach image (unchanged)
- clipboard has BOTH → let text paste normally AND attach image
The key change: preventDefault() is now only called when no text is
present (true screenshot paste), so the browser handles text insertion
naturally while addFiles() runs regardless.
Fixes the regression introduced by the #1620 fix. Closes#1620.