Original bug title:
VisualEditor: Inserting Media fails when caret is not positioned after initialization

And this is how to reproduce the issue:

• Go to https://www.mediawiki.org/wiki/Sandbox?veaction=edit
• Confirm the "This is our new tool ...."
• Reload the page
• Press "Insert"
• Press "Media" (dialog opens)
• Click one of the images.

Result:
Mozilla Firefox:

• POST https://www.mediawiki.org/w/api.php [HTTP/1.1 200 OK 281ms]
  • http://pastebin.de/124264
• TypeError: splice is undefined load.php:153
  • http://pastebin.de/124263
• Nothing happens except that the dialog is closed.
• Pressing "Insert" -> "Media" now does not open any dialog

Opera Next:

• Uncaught TypeError: Cannot read property 'apply' of undefined VM140:146
• Nothing happens except that the dialog is closed.
• Pressing "Insert" -> "Media" now does not open any dialog
• Stacktrace: http://pastebin.de/124262

Expected:

• Image inserted
• Being able to add further images to the page

Unrelated question:

• Why are you using FormData for this specific request?

Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=64759