git-rerere: detect unparsable conflicts

rerere did not detect the case where <<< === >>> markers did not match.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rerere.c

@@ -144,6 +144,11 @@ static int handle_file(const char *path,
 		fclose(out);
 	if (sha1)
 		SHA1_Final(sha1, &ctx);
+	if (hunk) {
+		if (output)
+			unlink(output);
+		return error("Could not parse conflict hunks in %s", path);
+	}
 	return hunk_no;
 }