patch 8.0.0074

Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.

src/json.c

@@ -328,7 +328,7 @@ json_encode_item(garray_T *gap, typval_T *val, int copyID, int options)
 	    break;
 #endif
 	case VAR_UNKNOWN:
-	    EMSG2(_(e_intern2), "json_encode_item()");
+	    internal_error("json_encode_item()");
 	    return FAIL;
     }
     return OK;