[staticanalysis]: Fix two uses of uninitialized variables

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Add missing va_end()

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Add assertion to pacify analyzer

This condition can't actually be hit, let's hint that's the case.

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Actually check errors on splice() of objects

We were using unsigned size when we should have been using signed,
this means we basically weren't checking for errors on write...ouch.

Luckily if we e.g. hit ENOSPC during a pull, the checksums wouldn't
match and we'd return an error anyways.  However when writing an
object, we'd end up silently ignoring it =/

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Fix some dead code

One was an unused variable, the other is actually dead because we
can't have mfile != NULL.

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Fix in_status_line

We need to end the status line *after* we've done a pull, as ostree
admin upgrade does.  Also add the correct in_status_line assignment.

https://bugzilla.gnome.org/show_bug.cgi?id=732020
[staticanalysis]: Delete an unused variable

https://bugzilla.gnome.org/show_bug.cgi?id=732020