message: Fix event handler
diff: @@ -21,7 +21,7 @@ using namespace visionaray;
  //-------------------------------------------------------------------------------------------------
  -// Event window
  +// Graphics view
  //
  @interface graphics_view : NSView
  @@ -377,7 +377,7 @@ using namespace visionaray;
  NSUInteger mf = [event modifierFlags] & NSEventModifierFlagDeviceIndependentFlagsMask;
  auto m = keyboard::map_cocoa_modifiers(mf);
  - mouse_event e(mouse::Move, p, b, m);
  + mouse_event e(mouse::ButtonUp, p, b, m);
  _viewer->call_on_mouse_up(e);
  }
  