libcamera: raspberry: Fix segfault in ~RPiCameraData()

The RPiCameraData class destructor tries to stop its ipa_ instance
without making sure it has been initialized.

If the RPiCameraData gets destroyed before its ipa_ member is
initialized, for example if the sensor initialization fails during the
match() function, a nullptr dereference segfault is triggered preventing
a graceful library teardown.

Fix this by checking for ipa_ to be initialized before stopping it.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/pipeline/raspberrypi/raspberrypi.cpp

@@ -304,7 +304,8 @@ public:
 		}
 
 		/* Stop the IPA proxy thread. */
-		ipa_->stop();
+		if (ipa_)
+			ipa_->stop();
 	}
 
 	void frameStarted(uint32_t sequence);