Iterates over the readable bytes of this buffer with the specified {@code processor} in descending order.
@return {@code -1} if the processor iterated to or beyond the beginning of the readable bytes.
The last-visited index If the {@link ByteProcessor#process(byte)} returned {@code false}.
Iterates over the readable bytes of this buffer with the specified {@code processor} in descending order.
@return {@code -1} if the processor iterated to or beyond the beginning of the readable bytes. The last-visited index If the {@link ByteProcessor#process(byte)} returned {@code false}.