Fixed bug #28293.

Occasionally mysqlbinlog --hexdump failed with error:
  ERROR 1064 (42000) at line ...: You have an error in your
  SQL syntax; check the manual that corresponds to your MySQL
  server version for the right syntax to use near
  'Query thread_id=... exec_time=... error_code=...

When the length of hexadecimal dump of binlog header was
divisible by 16, commentary sign '#' after header was lost.
The Log_event::print_header function has been modified to always
finish hexadecimal binlog header with "\n# ".

mysql-test/r/mysqlbinlog.result

@@ -312,4 +312,10 @@ DELIMITER ;
 # End of log file
 ROLLBACK /* added by mysqlbinlog */;
 /*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
+CREATE TABLE t1 (c1 CHAR(10));
+flush logs;
+INSERT INTO t1 VALUES ('0123456789');
+flush logs;
+DROP TABLE t1;
+# 	Query	thread_id=REMOVED	exec_time=REMOVED	error_code=REMOVED
 End of 5.0 tests

mysql-test/t/mysqlbinlog.test

@@ -203,4 +203,17 @@ flush logs;
 --replace_result $MYSQLTEST_VARDIR MYSQLTEST_VARDIR
 --exec $MYSQL_BINLOG --short-form --local-load=$MYSQLTEST_VARDIR/tmp/ $MYSQLTEST_VARDIR/log/master-bin.000009
 
+#
+# Bug#28293 missed '#' sign in the hex dump when the dump length
+# is divisible by 16.
+#
+
+CREATE TABLE t1 (c1 CHAR(10));
+# we need this for getting fixed timestamps inside of this test
+flush logs;
+INSERT INTO t1 VALUES ('0123456789');
+flush logs;
+DROP TABLE t1;
+--exec $MYSQL_BINLOG --hexdump --local-load=$MYSQLTEST_VARDIR/tmp/ $MYSQLTEST_VARDIR/log/master-bin.000011 | grep 'Query' | sed 's/[0-9]\{1,\}/REMOVED/g'
+
 --echo End of 5.0 tests

sql/log_event.cc

@@ -1001,11 +1001,15 @@ void Log_event::print_header(FILE* file, PRINT_EVENT_INFO* print_event_info)
     }
     *c= '\0';
 
-    /* Non-full last line */
     if (hex_string[0])
+    {
+      /* Non-full last line */
       fprintf(file, "# %8.8lx %-48.48s |%s|\n# ",
 	     (unsigned long) (hexdump_from + (i & 0xfffffff0)),
              hex_string, char_string);
+    }
+    else
+      fprintf(file, "# ");
   }
 }