remove header and footer of ListView when they are empty

taken from PR xamarin#10151

Author: heikow10

Xamarin.Forms.Platform.Android/Renderers/ListViewRenderer.cs

@@ -365,7 +365,14 @@ void UpdateFooter()
 			}
 
 			if (footer == null)
+			{
+				if (_footerView.ChildCount == 0)
+				{
+					AListView nativeListView = Control;
+					nativeListView.RemoveFooterView(_adapter.FooterView);
+				}
 				return;
+			}
 
 			if (_footerRenderer != null)
 				_footerRenderer.SetElement(footer);
@@ -397,7 +404,14 @@ void UpdateHeader()
 			}
 
 			if (header == null)
+			{
+				if (_headerView.ChildCount == 0)
+				{
+					AListView nativeListView = Control;
+					nativeListView.RemoveHeaderView(_adapter.HeaderView);
+				}
 				return;
+			}
 
 			if (_headerRenderer != null)
 				_headerRenderer.SetElement(header);