Decoded files contain a trailing null byte if bits_per_pixel is divisible by 8#3

Reproduction steps: ```bash # Create a file containing random data (shell expansion used for cross-platform compatibility) dd if=/dev/urandom bs=$((1024 * 1024)) count=2 of=data.bin # Encode with 8 bits per pixel ./bin2video -b 8 -s 8 -w 1920 -h 1080 -e -i data.bin -o data.bin.mp4 # Decode ./bin2video -d -i data.bin.mp4 -o data-out.bin ``` `data-out.bin` will be exactly 1 byte larger than `data.bin` and the extra byte will be a null byte.