Coverage improvement. Also, it's rude to die silently.

main.c

@@ -1185,9 +1185,6 @@ Lookup:
         default: // LCOV_EXCL_LINE
             BUG(VOCABULARY_TYPE_N_OVER_1000_NOT_BETWEEN_0_AND_3); // LCOV_EXCL_LINE
         }
-        if (!is_valid(game)) {
-            exit(1);
-        }
         switch (action(command)) {
         case GO_TERMINATE:
             return true;

tests/illformed.chk

@@ -91,6 +91,10 @@ down a gully.
 
 I see no grate here.
 
+> 23
+
+Sorry, I don't know the word "23".
+
 > eat building
 
 You are inside a building, a well house for a large spring.
@@ -618,7 +622,7 @@ Okay, "boo".
 
 > score
 
-You have garnered 27 out of a possible 430 points, using 117 turns.
+You have garnered 27 out of a possible 430 points, using 118 turns.
 
 > z
 
@@ -626,7 +630,7 @@ OK
 
 > score
 
-You have garnered 27 out of a possible 430 points, using 119 turns.
+You have garnered 27 out of a possible 430 points, using 120 turns.
 
 > quit keys
 

tests/illformed.log

@@ -16,6 +16,7 @@ back
 seed
 waste
 eat grate
+23
 eat building
 in
 # Z'ZZZ Word correct, but does nothing