android: post_processor_jpeg: Replace encoder_ nullptr check

Instead of simply returning if encoder_ is nullptr, fail hard
via an assertion. It is quite unlikely that encoder_ could only
be null as a result of a fatal bug in the code, so be loud about
the failure.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/android/jpeg/post_processor_jpeg.cpp

@@ -102,9 +102,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
 			       CameraBuffer *destination,
 			       Camera3RequestDescriptor *request)
 {
-	if (!encoder_)
-		return 0;
-
+	ASSERT(encoder_);
 	ASSERT(destination->numPlanes() == 1);
 
 	const CameraMetadata &requestMetadata = request->settings_;