Fix iterator for wc6 checking relearn

The .Remove was tampering with the same variable that the foreach was
iterating over, causing exceptions. By casting to a WC6[], the List<WC6>
can be altered and the array is iterated over instead.

Legality/Checks.cs

@@ -776,7 +776,7 @@ private LegalityCheck[] verifyRelearn()
             {
                 // Get WC6's that match
                 CardMatch = new List<WC6>(Legal.getValidWC6s(pk6));
-                foreach (var wc in CardMatch)
+                foreach (var wc in CardMatch.ToArray())
                 {
                     int[] moves = wc.RelearnMoves;
                     for (int i = 0; i < 4; i++)