Bug when not picking a profile picture

[KevKevR]

There's a bug in the code: while an user edits his profile picture, if he doesn't select a picture (eg. presses back before selecting a picture), the code doesn't properly handle a null image. This occurs in edit_profile.dart, with the _imageSelected attribute.

• [x] Add a null check before parsing the image. https://github.com/danielxjean/EngLife/blob/fda91e2848d893342fd1ee3600af9230403bff4e/eng_life/lib/screens/home/home_screens/edit_profile.dart#L46-L48

Edit: There was another line where there needed a null check. See lines affected in #87.