tools lib traceevent: Fix a risk for doing free on uninitialized pointer

Fix a risk of doing free on an uninitialized pointer.

This was found using a static code analysis program called cppcheck.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Link: http://lkml.kernel.org/r/1403608150-13037-1-git-send-email-rickard_strandqvist@spectrumdigital.se


Signed-off-by: Jiri Olsa <jolsa@kernel.org>