Fix: Prevents usage of wrong contexts in DepQuant

The suggested changes fix the following two issues:

[1]
For blocks with width>32 or height>32, the scan created in initRom()
(file Rom.cpp) are only valid for the non-zero-out region. However, in
Rom::xInitScanArrays() (file DepQuant.cpp), the zero-out region is also
used. This has the effect that the array raster2id[] contains wrong
values. As a consequence, wrong neighboring positions cpos[] are derived.

Even though a previous fix (fix #161) ensures that the positions are
clipped to a value inside the subblock, these positions could still be
wrong. It is suggested to fix the issue by correctly considering the
zero-out regions for larger blocks (which is the actual source of the problem).

[2]
In State::updateStateEOS(..), the array m_absLevelAndCtxInit should be
set equal to zero if a skipped subblock is selected. Otherwise, it could
be possible lead to a usage of wrongs contexts for following transform
coefficients.

In Rom::xInitScanArrays()