qcam: Clear the pool of free requests upon stopCapture()

To enable reusing Request objects, we kept a pool of free Requests. This
pool was not cleared upon stopping capture, however, which caused a
segfault when switching to another camera. Fix this by clearing the
Request pool on stopCapture().

Fixes: c753223ad6 ("libcamera, android, cam, gstreamer, qcam, v4l2: Reuse Request")
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>

src/qcam/main_window.cpp

@@ -579,6 +579,7 @@ void MainWindow::stopCapture()
 	mappedBuffers_.clear();
 
 	requests_.clear();
+	freeQueue_.clear();
 
 	delete allocator_;