RAR5 reader: invalid window buffer read in E8E9 filter

RAR5 reader: invalid window buffer read in E8E9 filter

The E8E9 filter was accessing the window buffer with a direct memory
read. But since the window buffer is a circular buffer, some of its data
can span between the end of the buffer and beginning of the buffer. This
means that accessing the window buffer needs to be done always by a
reading function that is aware of the fact that the window buffer is
circular.

The commit changes direct memory read to the access through the
circular_memcpy() function.

This fixes some edge cases when the E8E9 filter data (4 bytes) is
spanned between the end of the window buffer and the beginning of the
buffer. This situation can happen in archives compressed with a small
dictionary size.