While a SCH_SHEET does indeed have a SCH_SHEET parent, it's not one of
the children that gets added as a CHT_MODIFY of its parent.
Also fixes a bug where the newly drawn sheet gets removed from the
preview before running the dialog.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/14976
The connection graph should only be updated within the commit structure
because this is the only time the connectivity should be changed. We
want any connectivity changes to be included in the commit as well, so
this should be stored prior to the undo/redo list mods
Jeff Young
Seth Hillbrand