Fix flipped clipper2 ifdef

Fix flipped clipper2 ifdef

modules/navigation_2d/2d/godot_navigation_server_2d.cpp

@@ -1197,7 +1197,7 @@ COMMAND_1(free, RID, p_object) {
 		ERR_FAIL_NULL(parser);
 
 		generator_parsers.erase(parser);
-#ifndef CLIPPER2_ENABLED
+#ifdef CLIPPER2_ENABLED
 		NavMeshGenerator2D::get_singleton()->set_generator_parsers(generator_parsers);
 #endif
 		geometry_parser_owner.free(parser->self);