Fix 1987/lievaart - check for invalid input

It was documented that the program detected invalid input but it
actually (now - it used to work) printed in an infinite loop 'You:'. Now
doing invalid input forfeits the game which is better than flooding the
screen. It is not yet clear if it should act like you put in 99 (see the
README.md for details) so this is in bugs.md just in case. If it is
supposed to just skip a move then this can be fixed but otherwise it can
be removed from bugs.md without any change in the code. This fix applies
to both versions, the one with the board display and the original entry
(with contest restrictions on size of code).

bugs.md

@@ -537,12 +537,16 @@ or any others.
 # 1987
 
 ## [1987/lievaart](1987/lievaart/lievaart.c) ([README.md](1987/lievaart/README.md))
-## STATUS: INABIAF - please **DO NOT** fix
+## STATUS: possible bug (possibly depending on system) - please help test and if necessary fix
 
-Two issues to be aware of: if you input invalid input (as in invalid characters
-like `.`) it might enter an infinite loop printing the same thing over and over.
-Also if you don't enter a valid number it will prompt you again.
+Cody fixed this to not enter an infinite loop (it was documented to detect this
+but it no longer worked). However this will forfeit the game for the user and
+it's not clear at this time if it was supposed to just act like you input `99`
+(see the README.md for details here) but that seems probable.
 
+Another issue might be that certain input when prompted for input will just
+prompt you again for input but it might be that I (Cody) do not remember how to
+play the game and it's expected this way.
 
 # 1988