fallback: incorrect check after AllocateZeroPool()
fallback: incorrect check after AllocateZeroPool()

After calling AllocateZeroPool() we must check the returned pointer.

Fixes: 3ce517fdbb4e ("Add a fallback loader for when shim is invoked as BOOTX64.EFI")
Signed-off-by: Heinrich Schuchardt <d0f16556e4bb5a699e5016a06ebfc6cd472096d1@canonical.com>

rhinstaller/shim,rhinstaller/shim,rhinstaller/shim