Don't show section headers whose size is zero

Author: yimingtang

Classes/CSStickyHeaderFlowLayout.m

@@ -151,11 +151,13 @@ - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
                 header = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader
                                                               atIndexPath:[NSIndexPath indexPathForItem:0 inSection:indexPath.section]];
 
-                if (header) {
+                if (!CGSizeEqualToSize(CGSizeZero, header.frame.size)) {
                     [allItems addObject:header];
                 }
             }
-            [self updateHeaderAttributes:header lastCellAttributes:lastCells[indexPathKey]];
+            if (!CGSizeEqualToSize(CGSizeZero, header.frame.size)) {
+                [self updateHeaderAttributes:header lastCellAttributes:lastCells[indexPathKey]];
+            }
         }];
     }