It shouldn't be zero, but if the 'perf probe' on getname_flags() (or
elsewhere in the future we need to probe to catch the pathname for
syscalls like 'open' being copied from userspace to the kernel) is
misplaced somehow, then we will end up not allocating space and trying
to copy the "" empty string to ttrace->filename.name, causing a
segfault, fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-c4f1t6sx1nczuzop19r5si5s@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>