Adds a guard on null input before invalidate_pixel_data.
Adds a guard on null input before invalidate_pixel_data.

Matches an equivalent guard on set_pixel_data line 350.

This resolves a repeatable null pointer dereference on export from kdenlive when movit effects are
used. Did not investigate why the input associated with a provider would be null.

j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt