migration: Fix parse_ramblock() on overwritten retvals

migration: Fix parse_ramblock() on overwritten retvals

It's possible that some errors can be overwritten with success retval later
on, and then ignored.  Always capture all errors and report.

Reported by Coverity 1522861, but actually I spot one more in the same
function.

Fixes: CID 1522861
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231017203855.298260-1-peterx@redhat.com>