Fix comments and indentation in .gdshaderinc files

Fixes godotengine#78205
The handling of comments and indentation in the shader editor
wasn't considering shader include files.

(cherry picked from commit 71b8a9d)

editor/plugins/text_shader_editor.cpp

@@ -646,13 +646,13 @@ void TextShaderEditor::_menu_option(int p_option) {
 			shader_editor->move_lines_down();
 		} break;
 		case EDIT_INDENT: {
-			if (shader.is_null()) {
+			if (shader.is_null() && shader_inc.is_null()) {
 				return;
 			}
 			shader_editor->get_text_editor()->indent_lines();
 		} break;
 		case EDIT_UNINDENT: {
-			if (shader.is_null()) {
+			if (shader.is_null() && shader_inc.is_null()) {
 				return;
 			}
 			shader_editor->get_text_editor()->unindent_lines();
@@ -668,12 +668,10 @@ void TextShaderEditor::_menu_option(int p_option) {
 			shader_editor->get_text_editor()->set_line_wrapping_mode(wrap == TextEdit::LINE_WRAPPING_BOUNDARY ? TextEdit::LINE_WRAPPING_NONE : TextEdit::LINE_WRAPPING_BOUNDARY);
 		} break;
 		case EDIT_TOGGLE_COMMENT: {
-			if (shader.is_null()) {
+			if (shader.is_null() && shader_inc.is_null()) {
 				return;
 			}
-
 			shader_editor->toggle_inline_comment("//");
-
 		} break;
 		case EDIT_COMPLETE: {
 			shader_editor->get_text_editor()->request_code_completion();