postprocess: fix empty filename for UVC cameras

filename printed to stdout is used to bind to open filename
button. Without this nothing opened, when button was clicked.

data/postprocess.sh

@@ -33,6 +33,7 @@ MAIN_PICTURE="$BURST_DIR"/1
 if [ -f "$MAIN_PICTURE.jpg" ]; then
   # Just move over the main jpeg if this was a YUV capture
   cp "$MAIN_PICTURE.jpg" "$TARGET_NAME.jpg"
+  echo "$TARGET_NAME.jpg"
 
   # Clean up the temp dir containing the burst
   rm -rf "$BURST_DIR"