shim: Fix a NULL pointer dereference caused by start not being set
shim: Fix a NULL pointer dereference caused by start not being set

Commit 018b74d2d69 ("shim: attempt to improve the argument handling") added
added workarounds for a couple of LoadOption problems on some systems, but
introduced a regression since the is_our_path() function can be called with
a NULL start UCS-2 string.

If there's only one string, set start to the start of LoadOptions.

Signed-off-by: Javier Martinez Canillas <8fdf2abf85d34ea8f3f979ef25dc1f25d94aca29@redhat.com>

rhinstaller/shim,rhinstaller/shim,rhinstaller/shim