tools lib traceevent: Handle NULL comm name

It is possible that a pid has no associated comm attached to it, although it
can still be passed to pevent_register_comm().

But if comm is NULL, it will cause strdup() to segfault. To prevent this
from happening, if comm is NULL use the default "<...>" name for the
pid.

Signed-off-by: Josef Bacik <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Link: http://lkml.kernel.org/p/[e-mail]
Signed-off-by: Steven Rostedt <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/traceevent/event-parse.c

···
 	if (!item)
 		return -1;
 
-	item->comm = strdup(comm);
+	if (comm)
+		item->comm = strdup(comm);
+	else
+		item->comm = strdup("<...>");
 	if (!item->comm) {
 		free(item);
 		return -1;