fix xmltv generation when no block items are selected for guide (#1702)

.editorconfig

@@ -2,7 +2,7 @@
 [*]
 charset=utf-8
 end_of_line=lf
-trim_trailing_whitespace=false
+trim_trailing_whitespace=true
 insert_final_newline=false
 indent_style=space
 indent_size=4

ErsatzTV.Application/Channels/Commands/RefreshChannelDataHandler.cs

@@ -367,6 +367,11 @@ public class RefreshChannelDataHandler : IRequestHandler<RefreshChannelData>
             TimeSpan groupDuration = groupFinish - groupStart;
 
             var itemsToInclude = group.Filter(g => g.FillerKind is FillerKind.None).ToList();
+            if (itemsToInclude.Count == 0)
+            {
+                continue;
+            }
+
             TimeSpan perItem = groupDuration / itemsToInclude.Count;
 
             DateTimeOffset currentStart = new DateTimeOffset(groupStart, TimeSpan.Zero).ToLocalTime();