grid flatten: fix corner case when chunk shrinks to zero area

wrong integer cast caused endless iterator

nested/src/grid/flatten.rs

@@ -197,12 +197,12 @@ where
 
         let old_limit = self.limit;
         self.limit = Point2::new(
-            (0..=top_range.end().x as usize)
-                .map(|x| col_widths.get(x).unwrap_or(&0))
+            (0..=top_range.end().x)
+                .map(|x| col_widths.get(x as usize).unwrap_or(&0))
                 .sum::<i16>()
                 - 1,
-            (0..=top_range.end().y as usize)
-                .map(|y| row_heights.get(y).unwrap_or(&0))
+            (0..=top_range.end().y)
+                .map(|y| row_heights.get(y as usize).unwrap_or(&0))
                 .sum::<i16>()
                 - 1,
         );

nested/src/sequence/flatten.rs

@@ -65,7 +65,6 @@ where
     }
 }
 
-/* TODO: remove unused projection args (bot-views) if they get replaced by a new viewport  */
 impl<Item> Flatten<Item>
 where
     Item: 'static,
@@ -163,11 +162,9 @@ where
 
         let old_length = self.length;
         self.length = cur_offset;
-/* FIXXME: causes hangup
-        if self.length < old_length {
-            dirty_idx.extend(self.length..old_length);
-        }
-        */
+
+        dirty_idx.extend(self.length..old_length);
+
         dirty_idx
     }