Preserve the detached video dialog size when changing tools

The relayout to handle the changed subtoolbar size was fitting the
dialog to the size of the video, which was rather undesirable.

aegisub/src/video_display.cpp

@@ -414,7 +414,13 @@ void VideoDisplay::SetTool(std::unique_ptr<VisualToolBase> new_tool) {
 	tool->SetToolbar(toolBar);
 
 	// Update size as the new typesetting tool may have changed the subtoolbar size
+	if (!freeSize)
 		UpdateSize();
+	else {
+		// UpdateSize fits the window to the video, which we don't want to do
+		GetGrandParent()->Layout();
+		tool->SetDisplayArea(viewport_left, viewport_top, viewport_width, viewport_height);
+	}
 }
 
 bool VideoDisplay::ToolIsType(std::type_info const& type) const {