Fixed multiple materials obj X3D export (#6102)

Author: omichel

src/webots/nodes/WbCadShape.cpp

@@ -268,11 +268,7 @@ QStringList WbCadShape::objMaterialList(const QString &url) const {
       if (!cleanLine.startsWith("mtllib"))
         continue;
 
-      cleanLine = cleanLine.replace("mtllib ", "").trimmed();
-      cleanLine = cleanLine.replace("\"", "");
-      materials << cleanLine.split(".mtl ", Qt::SkipEmptyParts);
-      for (int i = 0; i < materials.size() - 1; i++)  // the last item still have '.mtl'
-        materials[i] += ".mtl";
+      materials << cleanLine.replace("mtllib ", "").replace("\"", "").trimmed();
     }
   } else
     warn(tr("File '%1' cannot be read.").arg(url));