Fix 2 issues with Profile->Edit Environment dialog

1. Correctly handle when user removes all lines
2. Correctly handle when user OKs Edit Env dialog and then reopens same dialog before closing Edit Profile dialog.

Thanks to ahmadsamir for patch.

Differential Revision: https://phabricator.kde.org/D8921

(cherry picked from commit eaccb7dc612e385f38ed5ca01281f28f151120fc)