GCC 4.4 compatibility: explicit std::reference_wrapper constructor.

src/MagnumPlugins/ObjImporter/ObjImporter.cpp

@@ -424,9 +424,9 @@ std::optional<MeshData3D> ObjImporter::doMesh3D(UnsignedInt id) {
     if(!normalIndices.empty() || !textureCoordinateIndices.empty()) {
         std::vector<std::reference_wrapper<std::vector<UnsignedInt>>> arrays;
         arrays.reserve(3);
-        arrays.push_back(positionIndices);
-        if(!normalIndices.empty()) arrays.push_back(normalIndices);
-        if(!textureCoordinateIndices.empty()) arrays.push_back(textureCoordinateIndices);
+        arrays.push_back(std::ref(positionIndices));
+        if(!normalIndices.empty()) arrays.push_back(std::ref(normalIndices));
+        if(!textureCoordinateIndices.empty()) arrays.push_back(std::ref(textureCoordinateIndices));
         indices = MeshTools::combineIndexArrays(arrays);
 
         /* Reindex data arrays */