Dispose render image in the case of no bitmap caching

When Bitmap caching is not enabled, a new image is created for each
render. Thus we need to ensure that, if a previous image has been
renderered, it is disposed first.

Flag: NONE host-only change
Bug: N/A
Test: test added
Change-Id: I9edc944650ca1da0bbcc3cb32cc40b3c1ba707c7
2 files changed