Clean up server rendered cursor logic

Variables were reused a bit too heavily and it was possible to get
the logic at a point where the server would try to render a cursor
where it wasn't needed, and the empty update rect would cause a
crash. Clear things up by introducing some more explicit variables.
diff --git a/common/rfb/VNCSConnectionST.h b/common/rfb/VNCSConnectionST.h
index 978879f..bc6ae5b 100644
--- a/common/rfb/VNCSConnectionST.h
+++ b/common/rfb/VNCSConnectionST.h
@@ -196,8 +196,8 @@
     VNCServerST* server;
     SimpleUpdateTracker updates;
     Region requested;
-    bool drawRenderedCursor, removeRenderedCursor;
-    Rect renderedCursorRect;
+    bool updateRenderedCursor, removeRenderedCursor;
+    Region damagedCursorRegion;
     bool continuousUpdates;
     Region cuRegion;
     EncodeManager encodeManager;