Update src/Beutl.Operators/Source/SourceVideoOperator.cs

Co-authored-by: Copilot <[email protected]>

Author: yuto-trd

src/Beutl.Operators/Source/SourceVideoOperator.cs

@@ -40,15 +40,12 @@ protected override void OnDetachedFromHierarchy(in HierarchyAttachmentEventArgs
     {
         base.OnDetachedFromHierarchy(args);
 
-        if (Value is { } value)
+        if (Value is { } value && _handler != null)
         {
-            if (_handler != null)
-            {
-                value.Source.Edited -= _handler;
-                value.OffsetPosition.Edited -= _handler;
-                value.Speed.Edited -= _handler;
-                value.IsLoop.Edited -= _handler;
-            }
+            value.Source.Edited -= _handler;
+            value.OffsetPosition.Edited -= _handler;
+            value.Speed.Edited -= _handler;
+            value.IsLoop.Edited -= _handler;
         }
 
         _handler = null;