Drag'n'drop bundle material to user material bugs

Tested with Qt Design Studio 3.8 built with Qt 6.3.2 (snapshot 3)

Bug 1:

• When you drag-n-drop bundle material from Material Library -field to Library -field, the Material Browser -view scrolls automatically down. This happens with both kits 5.15 and 6.3

Bug 2:

• When the bundle material is added to user materials, the bundle material goes invisible and does not show in the 3D object or in the Materials -field in the Material Browser -view. The warning message for the missing bundle material is shown in the picture below
• NOTE: this happens if using the project with Qt 5.15 kit. Qt 6.3 kit worked.
  

Bug 3:

• If the Material Browser -window is small, you cannot drag-n-drop the materials at the bottom of the Material Library to the Material -field, because you cannot use mouse scroll to go back up, while holding the material. Only way to add materials from the bottom by dragging is to drag the material to the 3D -view or by expanding the Material Browser -window, so the Library -field is visible. This happens with both kits 5.15 and 6.3