When saving blend files close any menus that might be open, show
"waiting" mouse cursor right away, before creating preview.
When you select "Save" from the File menu that menu will remain open until the saving process is complete, which can make blender look temporarily broken. This patch closes any open menus early in the saving process. Saving also currently sets and unset a "waiting" mouse cursor, but doesn't start this until after thumbnail creation. This patch moves that to before this happens so the wait cursor is shown during that part of the process to.
Because of these changes are to the greater process of saving, this patch also removes similar calls inside blend_file_thumb_from_screenshot since that is inside the parent the process.