text_area: fix interplay of shift with selection

Without this patch, the text area would mistakenly delete the characters
types after placing the cursor with the mouse as soon as shift is used
as modifier.

repos/gems/src/app/text_area/dialog.cc

@@ -472,8 +472,10 @@ void Dialog::handle_input_event(Input::Event const &event)
 
 		if (shift_key(key)) {
 			_shift = true;
-			if (!_selection.defined())
+			if (!_selection.defined()) {
 				_selection.start.construct(_cursor);
+				_selection.end.destruct();
+			}
 		}
 
 		if (control_key(key))