Add check for capture when draggable manipulator releases

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/Draggable.cs

         void OnMouseUp(MouseUpEvent evt)
         {
             m_Active = false;
-            target.ReleaseMouseCapture();
+
+            if (target.HasMouseCapture())
+            {
+                target.ReleaseMouseCapture();
+            }
+
             evt.StopPropagation();
         }
     }