Blender Git Loki

Fix T69921: VSE - Waveforms unnecessary redrawn on offset change

Waveform is freed in `sound_load_audio()` when sound length is `queried by BKE_sound_info_get()`.

Add argument free_waveform, so `BKE_sound_info_get()` can skip waveform freeing, as it is not expected to alter sound.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D6053