Fix clear records in IODB

[bsalomon, 2012-08-16 21:32:36]

IODB clears had two issues:

1) If the passed rt is not NULL and rect is NULL the implied rect is the bounds
of the passed rt, not the current rt

2) When the passed rt is NULL we store NULL in the clear record. However, at
playback the current RT may not be the same as record time. We don't record the
current RT into saved draw until the first draw that uses the current draw state
(assuming such a draw occurs).

With this change we get the bounds of the correct RT when the rect is NULL and
we always record a non-NULL RT.

[robertphillips, 2012-08-17 13:42:24]

LGTM

[bsalomon, 2012-08-17 13:43:27]

Committed as r5148