h264_encrypt::_apply_padding() - fixed warning: comparison of integers of different signs

[inobelar]

gcc 13.2.0 produces the next warning: comparison of integers of different signs: 'int' and 'size_t' (since i is int, and compared over size_t inside for loop: i < paddint_byte_count). This small PR fixes it.

I also replaced uint8_t and size_t by equivalent types: guint8 and gsize, due to passed arguments types:

• &naul->data[payload_offset] is guint8*
• payload_size, map_info->maxsize are gsize

[ReFormationPro]

I compiled the project after configuring it with meson setup build -Dwarning_level=2 -Dwerror=true -Dc_std=gnu99. At warning level 3, GLib conflicts with ISO-C for a warning categorized as "pedantic" so I targeted level 2.

There were some similar errors, I fixed them too.

I did not change the standard types to g* types yet. I am thinking of using one set of types over the entire project. Maybe I should change them all together.