h4-section-patch: Fix oversized error checking

Somehow the code to check for oversized sections got moved
past the code that actually replaces section contents. This
is what I get for not sleeping. The result is that the code
would either try to update the section and then print the
error prior to saving the firmware, or outright crash due
to out-of-bounds memory access. Either way, fix things to
handle this case gracefully.

Signed-off-by: evilwombat <evilwombat@server.fake>