Close shader under cursor when middle mouse clicking in editor list

Previously middle mouse clicking resulted in the currently selected
file to be closed, which is not the behavior commonly expected.

editor/plugins/shader_editor_plugin.cpp

@@ -1376,11 +1376,10 @@ void ShaderEditorPlugin::_shader_list_clicked(int p_item, Vector2 p_local_mouse_
 }
 
 void ShaderEditorPlugin::_close_shader(int p_index) {
-	int index = shader_tabs->get_current_tab();
-	ERR_FAIL_INDEX(index, shader_tabs->get_tab_count());
-	Control *c = shader_tabs->get_tab_control(index);
+	ERR_FAIL_INDEX(p_index, shader_tabs->get_tab_count());
+	Control *c = shader_tabs->get_tab_control(p_index);
 	memdelete(c);
-	edited_shaders.remove_at(index);
+	edited_shaders.remove_at(p_index);
 	_update_shader_list();
 	EditorNode::get_singleton()->get_undo_redo()->clear_history(); // To prevent undo on deleted graphs.
 }