perf tools: fix thread_map__new_by_pid_str() memory leak in error path

The namelist array (including its content) was not freed if we fail to
realloc a new 'threads' structure.

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Link: http://lkml.kernel.org/r/1337952109-31995-1-git-send-email-fbuihuu@gmail.com


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