ide: Treat read/write beyond end as invalid

The block layer fails such reads and writes just fine.  However, they
then get treated like valid operations that fail: the error action
gets executed.  Unwanted; reporting the error to the guest is the only
sensible action.

Reject them before passing them to the block layer.  This bypasses the
error action and I/O accounting.  Not quite correct for DMA, because
DMA can fail after some success, and when that happens, the part that
succeeded isn't counted.  Tolerable, because I/O accounting is an
inconsistent mess anyway.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
