ChannelFiller: avoid race conditions with the cache

When caching things, we need to be very careful to disallow the caller
from overwriting our carefully recorded offsets.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
PlaneSeparator: fix strip offsets

When reading multiple strips successively, the start offset needs to be
set to, not increased by, i * rowstride... ;-)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #98 from scifio/fix-striped-reading

Fix striped reading