Ensure that we keep the window at the same display when resizing

Use wxRect::Inflate(), which preserves the position of the center of the
rectangle, instead of just changing its size, which could the position
of the center and result in the window snapping back to the previous
display (and, even more catastrophically, then being moved back to the
new one when handling the resulting WM_DPICHANGED and so on forever).

src/msw/nonownedwnd.cpp

@@ -292,9 +292,15 @@ bool wxNonOwnedWindow::HandleDPIChange(const wxSize& newDPI, const wxRect& newRe
         // size is usually a decent guess, it's typically not exactly correct.
         // We can't always do much better, but at least ensure that the window
         // is still big enough to show its contents.
-        wxSize newSize = newRect.GetSize();
-        newSize.IncTo(GetBestSize());
-        SetSize(wxRect(newRect.GetPosition(), newSize));
+        wxSize diff = GetBestSize() - newRect.GetSize();
+        diff.IncTo(wxSize(0, 0));
+
+        // Use wxRect::Inflate() to ensure that the center of the (possibly)
+        // bigger rectangle is at the same position as the center of the
+        // proposed one, to prevent moving the window back to the old display
+        // from which it might have been just moved to this one, as doing this
+        // would result in an infinite stream of WM_DPICHANGED messages.
+        SetSize(newRect.Inflate(diff.x, diff.y));
     }
 
     Refresh();