Handle the SRCLINE_UNKNOWN case correctly when processing "srcfile".

Commiter note:

We can't just free it, as it was't allocated via malloc, its a guard
variable.
Reported-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20150811133655.GC4524@tassilo.jf.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>