[Fix]: Form submission on Image upload

When only file(image) is uploaded and submitted in : 
1. http://demo.eden.sahanafoundation.org/eden/hms/hospital/1/image (Add Photo)
2. http://demo.eden.sahanafoundation.org/eden/doc/image/create
ERROR - "Either file upload or image URL required!"
Though url is not a required field.
Not correct - URL is a valid alternative, and file can be NULL in those cases