[c-host] inform the client if we have positional cursor information

c-host/include/interface/capture.h

@@ -61,6 +61,7 @@ CaptureFrame;
 
 typedef struct CapturePointer
 {
+  bool          positionUpdate;
   int           x, y;
   bool          visible;
 
@@ -94,4 +95,4 @@ typedef struct CaptureInterface
   CaptureResult (*waitFrame )(CaptureFrame * frame);
   CaptureResult (*getFrame  )(FrameBuffer  * frame);
 }
-CaptureInterface;
+CaptureInterface;