Allow unselection when no solution is found in matrix solver

[Pxx500]

Suggestion

Allow the option to unselect one of the selected unrestricted items in the right side of the notification that no solution was found

Each time I accidentally select a wrong item I have to disable and re-enable matrix solver to try again (which removes all of my previous selections, in this screen it's not a big problem but when chains get much longer it can get problematic)