Backport fix for escaping multibyte characters. (Bug #9864)

libmysql/libmysql.c:
  Backport fix for escaping multibyte characters from 4.1

libmysql/libmysql.c

@@ -3228,6 +3228,23 @@ mysql_sub_escape_string(CHARSET_INFO *charset_info, char *to,
       from--;
       continue;
     }
+    /*
+     If the next character appears to begin a multi-byte character, we
+     escape that first byte of that apparent multi-byte character. (The
+     character just looks like a multi-byte character -- if it were actually
+     a multi-byte character, it would have been passed through in the test
+     above.)
+
+     Without this check, we can create a problem by converting an invalid
+     multi-byte character into a valid one. For example, 0xbf27 is not
+     a valid GBK character, but 0xbf5c is. (0x27 = ', 0x5c = \)
+    */
+    if (use_mb_flag && (l= my_mbcharlen(charset_info, *from)) > 1)
+    {
+      *to++= '\\';
+      *to++= *from;
+      continue;
+    }
 #endif
     switch (*from) {
     case 0:				/* Must be escaped for 'mysql' */
@@ -3300,6 +3317,23 @@ mysql_odbc_escape_string(MYSQL *mysql,
 	from--;
 	continue;
       }
+      /*
+       If the next character appears to begin a multi-byte character, we
+       escape that first byte of that apparent multi-byte character. (The
+       character just looks like a multi-byte character -- if it were actually
+       a multi-byte character, it would have been passed through in the test
+       above.)
+
+       Without this check, we can create a problem by converting an invalid
+       multi-byte character into a valid one. For example, 0xbf27 is not
+       a valid GBK character, but 0xbf5c is. (0x27 = ', 0x5c = \)
+      */
+      if (use_mb_flag && (l= my_mbcharlen(mysql->charset, *from)) > 1)
+      {
+        *to++= '\\';
+        *to++= *from;
+        continue;
+      }
     }
 #endif
     switch (*from) {