tracing: Fix race where eprobes can be called before the event

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix race where eprobes can be called before the event

The flag that tells the event to call its triggers after reading the event

is set for eprobes after the eprobe is enabled. This leads to a race where

the eprobe may be triggered at the beginning of the event where the record

information is NULL. The eprobe then dereferences the NULL record causing

a NULL kernel pointer bug.

Test for a NULL record to keep this from happening.