qemu_opts_foreach() runs its callback with the error location set to
the option's location.  Any errors the callback reports use the
option's location automatically.

Commit 90998d58 moved the actual error reporting from "inside"
qemu_opts_foreach() to after it.  Here's a typical hunk:

	 if (qemu_opts_foreach(qemu_find_opts("object"),
    -                          object_create,
    -                          object_create_initial, NULL)) {
    +                          user_creatable_add_opts_foreach,
    +                          object_create_initial, &err)) {
    +        error_report_err(err);
	     exit(1);
	 }

Before, object_create() reports from within qemu_opts_foreach(), using
the option's location.  Afterwards, we do it after
qemu_opts_foreach(), using whatever location happens to be current
there.  Commonly a "none" location.

This is because Error objects don't have location information.
Problematic.

Reproducer:

    $ qemu-system-x86_64 -nodefaults -display none -object secret,id=foo,foo=bar
    qemu-system-x86_64: Property '.foo' not found

Note no location.  This commit restores it:

    qemu-system-x86_64: -object secret,id=foo,foo=bar: Property '.foo' not found

Note that the qemu_opts_foreach() bug just fixed could mask the bug
here: if the location it leaves dangling hasn't been clobbered, yet,
it's the correct one.
Reported-by: NEric Blake <eblake@redhat.com>
Cc: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <1461767349-15329-4-git-send-email-armbru@redhat.com>
Reviewed-by: NDaniel P. Berrange <berrange@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
[Paragraph on Error added to commit message]