Add missing increase of niter for FISTA

src/hotopy/optimize.py

@@ -315,6 +315,8 @@ class FISTA:
 
     @torch.no_grad()
     def step(self):
+        self.niter += 1
+
         # forward step: gradient decent step (note: gradients in y!)
         self.y_hat = self.y - self.tau * self.y.grad