Fix crash when modify parameter of visual shader

[xuhuisheng]

• Fixes: Visual Shader Crashes when Adjusting Float Parameter #112106

Issue Description

When changed parameter value of Visual Shader, we will trigger a "changed" signal and invoke VisualShaderEditor::_param_property_changed(). Notification chain is as follows:

• [1] visual_shader._set_preview_shader_parameter()
• [2] visual_shader.emit_changed(), trigger "changed" signal
• [3] ShaderMaterial::_shader_changed()
• [3] ShaderMaterial::notify_property_list_changed(), trigger "property_list_changed" signal
• [4] VisualShaderEditor::_update_preview_parameter_list()

In _update_preview_parameter_list(), we used get_shader_parameter_list() from RenderingServer to sync UI tree list. The problem is we need determine whether we need re-create parameter tree. Current behavior clean and re-create parameter tree all the time. But after re-created tree, VisualShaderEditor still want to focus to the previous selected node. But the tree is re-created, we cannot get the previous selected tree, so the select_node is nullptr, then crashed.

Solution

I checked the properties from RenderingServer and the current parameter list from Editor. If there is NO inserted or removed parameters, we donot need to re-create parameter tree. So we can prevent crash.

Also, I add a ERR_FAIL_NULL_MSG to prevent get_selected_node is null, that is for safe.