message: use rkcommon method instead of substring
diff: @@ -31,7 +31,7 @@ class AdvancedMaterialEditor
  for (auto &c : sourceMat->children()) {
  if (c.second->name() != "handles" && c.second->name() != skipParam) {
  // keep existing textures
  - if (c.second->name().substr(0, 4) == "map_")
  + if (beginsWith(c.second->name(), std::string("map_")))
  newMat->add(c.second);
  else
  newMat->child(c.second->name()).setValue(c.second->value());
  