Small fix

tools.py

@@ -128,6 +128,7 @@ class Main:
                 self.fit_avg.update_value(fit_error)
         else:
             roundness = 0
+            fit_error = -1
             max_int, num_pix = (0, 0)
             linearity = "No ions"
 
@@ -641,6 +642,9 @@ def dark_ions(image, coord, dist_factor):
         #     warnings.warn("Loss is too high... "
         #     "Try calculating a new factor value using calibrate() function.")
 
+    else:
+        loss = np.array([-1])
+
     return coord, loss.min()