When analysis_image is set to ANALYSISIMAGE_YCHANNEL but in_frame is
not populated (e.g., LocalCamera which captures directly to image),
get_y_image() returns nullptr. The code was dereferencing this null
pointer in DetectMotion and Blend calls, causing a segfault.
Now checks if y_image is valid before use and skips the operation
with a debug message if unavailable.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
b76a7c9640