[BUGFIX] "New record" button in Template mod broken

Recent browsers follow HTML5 standards for submitting image input
elements. The result is that the name of the image input element is
not submitted anymore, only the name with the x and y coordinates.
Checking for createExtension_x or createExtension being set makes the
button work again.

Change-Id: Id6424c44978be807c51bcdd842d11761d9aa947e
Resolves: #28455
Branches: 4.6, 4.5
Reviewed-on: http://review.typo3.org/4405
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog