Identify XButton1|2 release events when mouse is moving.

X11 has no special state for XButton1 and XButton2, so we need
to look at the global `mouseButtonState` and restore the buttons
after a mouse move.

Task-number: QTBUG-40148
Change-Id: I789f32b344cf7902b1c7aa6b7da7f20f32602be2
Reviewed-by: Alexander Volkov <[email protected]>
Reviewed-by: Shawn Rutledge <[email protected]>

Author: naufraghi

src/gui/kernel/qapplication_x11.cpp

@@ -4189,6 +4189,12 @@ static Qt::MouseButtons translateMouseButtons(int s)
         ret |= Qt::MidButton;
     if (s & Button3Mask)
         ret |= Qt::RightButton;
+    // X11 has no special state for XButton1 and XButton2, so we need to use
+    // the global state maintained between press and release.
+    if (mouseButtonState.testFlag(Qt::XButton1))
+        ret |= Qt::XButton1;
+    if (mouseButtonState.testFlag(Qt::XButton2))
+        ret |= Qt::XButton2;
     return ret;
 }