fixed a type signature error

example.cpp

@@ -703,6 +703,7 @@ void draw(NVGcontext *vg, float w, float h) {
     uiSetLayout(0,UI_LEFT|UI_TOP);
     uiSetMargins(0,600,10,0,0);
     uiSetSize(0,250,400);
+    uiSetSelfHandle(root);
     uiSetHandler(root, roothandler, UI_SCROLL|UI_BUTTON0_DOWN);
     
     int col = column(root);

oui.h

@@ -750,7 +750,7 @@ struct UIcontext {
     int extend_item;
     int last_timestamp;
     int last_click_timestamp;
-    int last_click_handle;
+    UIhandle last_click_handle;
     int clicks;
     
     int count;