Error-checking text fields, fixed small bugs

When a user attempts to create a new member without specifying a
username, email, or password, the dialog will close and a Toast message
will appear notifying them that those fields needed to be entered. I
also moved the segment of code that associated a profile_picture to the
current user so that it is only run after a succesful attempt is made to
create a new member. This was a problem before because a user could
attempt to create a new member without all the fields, and the segment
of code would still run.