crash on selection of an empty track

[aldo-aguilar]

repro: run reaper with kiwi, on the toolbar select "Track", select "Insert New Track", when this empty track is selected there is exception.

error: An invalid parameter was passed to a function that considers invalid parameters fatal.

source code: audio_pixel_block_t audio_pixel_block_t::get_pixels(), when calculating start_idx invalid arguments for clamp