Remove useless SinglePar update when scrolling in text

Using SinglePar does not majke sense here since the paragraph is not
modified and it might even not have a position yet.

This fixes a crash in BufferView::singleParUpdate, which is not
prepared (yet) to such situations.

src/Text.cpp

@@ -5344,7 +5344,7 @@ void Text::dispatch(Cursor & cur, FuncRequest & cmd)
 		bvcur.setCurrentFont();
 		if (cur.top() == old) {
 			// We didn't move one iota, so no need to update the screen.
-			cur.screenUpdateFlags(Update::SinglePar | Update::FitCursor);
+			cur.screenUpdateFlags(Update::FitCursor);
 			//cur.noScreenUpdate();
 			return;
 		}