bisect--helper: simplify exit code computation

We _already_ have a function to determine whether a given `enum
bisect_error` value is non-zero but still _actually_ indicates success.

Let's use it instead of duplicating the logic.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

builtin/bisect.c

@@ -1440,12 +1440,5 @@ int cmd_bisect(int argc, const char **argv, const char *prefix)
 		res = fn(argc, argv, prefix);
 	}
 
-	/*
-	 * Handle early success
-	 * From check_merge_bases > check_good_are_ancestors_of_bad > bisect_next_all
-	 */
-	if ((res == BISECT_INTERNAL_SUCCESS_MERGE_BASE) || (res == BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND))
-		res = BISECT_OK;
-
-	return -res;
+	return is_bisect_success(res) ? 0 : -res;
 }