updater: Fix the broken case for apply_patch_check().

It's valid to provide only 1 argument to apply_patch_check(). We
shouldn't fail the argument parsing.

Bug: 36541737
Test: recovery_component_test passes.
Test: recovery_component_test captures the failure without the fix.
Test: The previously failed update applies successfully.
Change-Id: Iee4c54ed33b877fc4885945b085341ec5c64f663