lib-mail: Fix out-of-bounds read when parsing an invalid email address

The included unit test doesn't fail, but running it with valgrind shows
"Invalid read of size 1" error.

Broken in d6737a1

Discovered by Aleksandar Nikolic of Cisco Talos

src/lib-mail/message-address.c

@@ -221,7 +221,8 @@ static int parse_addr_spec(struct message_address_parser_context *ctx)
 		/* end of input or parsing local-part failed */
 		ctx->addr.invalid_syntax = TRUE;
 	}
-	if (ret != 0 && *ctx->parser.data == '@') {
+	if (ret != 0 && ctx->parser.data != ctx->parser.end &&
+	    *ctx->parser.data == '@') {
 		ret2 = parse_domain(ctx);
 		if (ret2 <= 0)
 			ret = ret2;

src/lib-mail/test-message-address.c

@@ -198,6 +198,16 @@ static void test_message_address(void)
 		{ "<@>", "", "<INVALID_ROUTE:MISSING_MAILBOX@MISSING_DOMAIN>",
 		  { NULL, NULL, NULL, "", "", TRUE },
 		  { NULL, NULL, "INVALID_ROUTE", "MISSING_MAILBOX", "MISSING_DOMAIN", TRUE }, 0 },
+
+		/* Test against a out-of-bounds read bug - keep these two tests
+		   together in this same order: */
+		{ "aaaa@", "<aaaa>", "<aaaa@MISSING_DOMAIN>",
+		  { NULL, NULL, NULL, "aaaa", "", TRUE },
+		  { NULL, NULL, NULL, "aaaa", "MISSING_DOMAIN", TRUE }, 0 },
+		{ "a(aa", "", "<MISSING_MAILBOX@MISSING_DOMAIN>",
+		  { NULL, NULL, NULL, "", "", TRUE },
+		  { NULL, NULL, NULL, "MISSING_MAILBOX", "MISSING_DOMAIN", TRUE },
+		  TEST_MESSAGE_ADDRESS_FLAG_SKIP_LIST },
 	};
 	static struct message_address group_prefix = {
 		NULL, NULL, NULL, "group", NULL, FALSE