The form validate does not need to be called until we are done processin...

The form validate does not need to be called until we are done processing all of the images; this fixes the multiple image fields on the node creating multiple nodes bug; still need to handle multiple images within an image field.
@chrisschaub This comment outlines the issue fairly well: https://github.com/signalpoint/DrupalGap/issues/400#issuecomment-62406094

Essentially, if there is more than one image field, each call to _image_field_form_process() should recursively call itself (via the success callback) to process each image field. The final image field will be the stop case, and that success callback will proceed with the call to `form_validation()`.