MDEV-32458 ASAN unknown-crash in Inet6::ascii_to_fbt when casting character string to inet6

The condition checked the value of the leftmost byte before checking if
at least one byte is still available in the buffer.
Changing the order in the condition: check for a byte availability before
checking the byte value.

plugin/type_inet/mysql-test/type_inet/type_inet6.result

@@ -2330,3 +2330,14 @@ Warning	1292	Incorrect inet6 value: ''
 Warning	1292	Incorrect inet6 value: ''
 Warning	1292	Incorrect inet6 value: ''
 DROP TABLE t1;
+#
+# MDEV-32458 ASAN unknown-crash in Inet6::ascii_to_fbt when casting character string to inet6
+#
+CREATE TABLE t1 (c CHAR(3));
+INSERT INTO t1 VALUES ('1:0'),('00:');
+SELECT * FROM t1 WHERE c>CAST('::1' AS INET6);
+c
+Warnings:
+Warning	1292	Incorrect inet6 value: '1:0'
+Warning	1292	Incorrect inet6 value: '00:'
+DROP TABLE t1;

plugin/type_inet/mysql-test/type_inet/type_inet6.test

@@ -1686,3 +1686,13 @@ SELECT 1.00 + (b = a) AS f FROM t1 ORDER BY f;
 SELECT 1.00 + (b BETWEEN a AND '') AS f FROM t1 ORDER BY f;
 SELECT 1.00 + (b IN (a,'')) AS f FROM t1 ORDER BY f;
 DROP TABLE t1;
+
+
+--echo #
+--echo # MDEV-32458 ASAN unknown-crash in Inet6::ascii_to_fbt when casting character string to inet6
+--echo #
+
+CREATE TABLE t1 (c CHAR(3));
+INSERT INTO t1 VALUES ('1:0'),('00:');
+SELECT * FROM t1 WHERE c>CAST('::1' AS INET6);
+DROP TABLE t1;

plugin/type_inet/sql_type_inet.cc

@@ -229,7 +229,7 @@ bool Inet6::ascii_to_ipv6(const char *str, size_t str_length)
         continue;
       }
 
-      if (!*p || p >= str_end)
+      if (p >= str_end || !*p)
       {
         DBUG_PRINT("error", ("ascii_to_ipv6(%.*s): invalid IPv6 address: "
                              "ending at ':'.", (int) str_length, str));