Allow upscaling wxArtProvider bitmaps by integer scale factor

While upscaling the bitmaps by factors smaller than 2 results in truly
awful results, upscaling them by 2, or 3, is better on high DPI screens
than using tiny bitmaps that are difficult to read in high resolution,
so do scale them up in this case.

This finally makes wxBitmapBundleImplArt::GetBitmap() work as expected,
as it now returns the upscaled bitmap rather than the original small
bitmap in the middle of a bigger canvas.

src/common/artprov.cpp

@@ -309,7 +309,11 @@ wxArtProvider::RescaleOrResizeIfNeeded(wxBitmap& bmp, const wxSize& sizeNeeded)
         return;
 
 #if wxUSE_IMAGE
-    if ((bmp_w <= sizeNeeded.x) && (bmp_h <= sizeNeeded.y))
+    // Allow upscaling by an integer factor: this looks not too horribly and is
+    // needed to use reasonably-sized bitmaps in the code not yet updated to
+    // use wxBitmapBundle but using custom art providers.
+    if ((bmp_w <= sizeNeeded.x) && (bmp_h <= sizeNeeded.y) &&
+            (sizeNeeded.x % bmp_w || sizeNeeded.y % bmp_h))
     {
         // the caller wants default size, which is larger than
         // the image we have; to avoid degrading it visually by
@@ -319,7 +323,7 @@ wxArtProvider::RescaleOrResizeIfNeeded(wxBitmap& bmp, const wxSize& sizeNeeded)
         img.Resize(sizeNeeded, offset);
         bmp = wxBitmap(img);
     }
-    else // scale (down or mixed, but not up)
+    else // scale (down or mixed, but not up, or at least not by an int factor)
 #endif // wxUSE_IMAGE
     {
         wxBitmap::Rescale(bmp, sizeNeeded);