perf machine: Fix __machine__findnew_thread() error path

When thread__init_map_groups() fails, a new thread should be removed
from the rbtree since it's gonna be freed. Also update last match cache
only if the function succeeded.

Reported-by: David Ahern <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/machine.c

···
 	if (th != NULL) {
 		rb_link_node(&th->rb_node, parent, p);
 		rb_insert_color(&th->rb_node, &machine->threads);
-		machine->last_match = th;
 
 		/*
 		 * We have to initialize map_groups separately
···
 		 * leader and that would screwed the rb tree.
 		 */
 		if (thread__init_map_groups(th, machine)) {
+			rb_erase(&th->rb_node, &machine->threads);
 			thread__delete(th);
 			return NULL;
 		}
+
+		machine->last_match = th;
 	}
 
 	return th;