perf tools: Fix memory leak when synthesizing thread records

Checking default guest machine should be done before allocating event
structures otherwise it'll leak memory.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Link: http://lkml.kernel.org/r/87ob15tx6a.fsf@sejong.aot.lge.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>