revert placement change

Author: willmcgugan

src/textual/_compositor.py

@@ -630,10 +630,7 @@ def add_widget(
                     placement_scroll_offset = placement_offset - widget.scroll_offset
 
                     placements = [
-                        placement.process_offset(
-                            no_clip if styles.overlay == "screen" else size.region,
-                            placement_scroll_offset,
-                        )
+                        placement.process_offset(size.region, placement_scroll_offset)
                         for placement in placements
                     ]