behatnotneeded: is a style change

When you submit the form after uploading an image it removes the form
completely from the DOM so that the functions formStopProcessing() and
processingStop() never get to trigger.

I've added a processingStop() to the imagebrowser code directly - this
should be fine as mahara.js is called on every page so the function
will be presesnt.

Change-Id: I2ef6b44885e75c6f032557adacd920efbf4b1aa2
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>