Fix bug in tosc_reset

[cmoore42]

tosc_reset was operating on offsets based on the location of the format (o->format). When it came time to adjust the marker location to a multiple of 4 bytes it adjusted that index to a multiple of 4 bytes, which gives you a location aligned relative to o->format. But the location needs aligned relative to the entire buffer.

This change re-writes tosc_reset to operate entirely relative to the buffer start rather than to the start of the format.