Fix segfault when parsing arguments with no filename

When user doesn't specify a filename, or specifies '-h' first,
new_fw_image won't be set.

BUG=chromium-os:21568
TEST=emerge-${B} cypress-tools builds clean
  On device:
    cyapa_fw_update -h
  => prints help; no Segmentation fault

Change-Id: Iab8043587c99dede9a3a338175ebc61025fe2410
1 file changed