rts/Interpreter: Assert that TEST*_P discriminators are valid

rts/Interpreter.c

@@ -1785,6 +1785,7 @@ run_BCO:
         case bci_TESTLT_P: {
             unsigned int discr  = BCO_NEXT;
             int failto = BCO_GET_LARGE_ARG;
+            ASSERT(discr <= TAG_MASK);
             StgClosure* con = UNTAG_CLOSURE((StgClosure*)SpW(0));
             if (GET_TAG(con) >= discr) {
                 bciPtr = failto;
@@ -1795,6 +1796,7 @@ run_BCO:
         case bci_TESTEQ_P: {
             unsigned int discr  = BCO_NEXT;
             int failto = BCO_GET_LARGE_ARG;
+            ASSERT(discr <= TAG_MASK);
             StgClosure* con = UNTAG_CLOSURE((StgClosure*)SpW(0));
             if (GET_TAG(con) != discr) {
                 bciPtr = failto;