It's lining had started to fray and the seam ruptured. This is quite common problem with the linings but I show you an easy trick what you can do about it.
Just pick up a thread and needle. Make tiny stitches like this to close up the seam.
At the end no one can notice you fixed it and keep on wearing your dear old piece of cloth.
Besides; you wear it right side up and none sees inside if it is your first time and turns out a bit messy. Just make sure you sew far enough from the edge to prevent new fraying to happen soon.
See this to be done in another part of a cloth with different material here!