xcb: Fix QXcbCursor for secondary screen

QXcbCursor is created for each screen in a multiscreen setup. Make sure
xcb cursor context is created for all QXcbCursor instances otherwise
xcb can't load cursor for non-primary screens.

Amends commit 012132c60d

Pick-to: 6.5
Fixes: QTBUG-110434
Change-Id: I85da73a1069b681437b29c3e272d85f5d2dde130
Reviewed-by: Liang Qi <liang.qi@qt.io>

src/plugins/platforms/xcb/qxcbcursor.cpp

@@ -258,14 +258,14 @@ QXcbCursor::QXcbCursor(QXcbConnection *conn, QXcbScreen *screen)
     m_bitmapCache.setMaxCost(8);
 #endif
 
+    updateContext();
+
     if (cursorCount++)
         return;
 
     cursorFont = xcb_generate_id(xcb_connection());
     const char *cursorStr = "cursor";
     xcb_open_font(xcb_connection(), cursorFont, strlen(cursorStr), cursorStr);
-
-    updateContext();
 }
 
 QXcbCursor::~QXcbCursor()