Revert simplified if() in mysql-test/include/show_events.inc

mysql-test/include/show_events.inc

@@ -25,7 +25,9 @@ if ($binlog_file)
 
 --let $_statement= $_statement from $binlog_start
 
-if ($binlog_limit)
+# Cannot use if($binlog_limit) since the variable may begin with a 0
+
+if (`SELECT '$binlog_limit' <> ''`)
 {
   --let $_statement= $_statement limit $binlog_limit
 }