fdo#69282: sw: fix updating of page styles via SwDocShell::_LoadStyles()

SwDoc::CopyPageDesc() only copies master and left SwFrmFmt attributes,
but not first-master and first-left.  They will contain exactly the same
attributes as master and left but they still need to be copied...

(see also: that FIXME in pagedesc.hxx)

(regression from 75084f6c42c27dc95418df9cefed2fddfb26000e)

Change-Id: I3dcc3627708b5d6a477eb7fef76cf6c42c95c004
SwDoc::CopyPageDesc(): probably sending Modify for first too cannot hurt

Change-Id: I2056bee7555d3f6723ac374863187d82e4ad9edd