install.c: fix 'context->progress' should not be NULL
install.c: fix 'context->progress' should not be NULL

In determine_slot_errors() the step will begin only after checking for
available slots.
When determine_slot_errors() is called with no valid slot configuration,
it will goto the cleanup function and end a progress step that did not
begin, yet.

Fixed by beginning the progress step before checking.

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,jluebbe/rauc