BUG: don't compute minimum of binarised mask

gyral_structure/scripts/gs_mask

@@ -59,7 +59,7 @@ gyral_wm_mask = (dist_mask | thickness_mask) & (white_dist < 0)
 
 final_mask = (gyral_wm_mask | intersect_mask) & close_to_white_mask
 
-idx_deepest = np.unravel_index(dist_mask.argmin(), shape=dist_mask.shape)
+idx_deepest = np.unravel_index(white_dist.argmin(), shape=white_dist.shape)
 if final_mask[idx_deepest]:
     raise ValueError("Even the deepest white matter point was included in the gyral mask.")
 
@@ -69,7 +69,7 @@ filled = ndimage.binary_fill_holes(final_mask)
 if filled[idx_deepest]:
     # Filling holes in the gyral white matter also filled the deep white matter
     # Let's fix that
-    new_filled = filled - final_mask
+    new_filled = filled ^ final_mask
     labels, _ = ndimage.label(new_filled)
     filled[labels[idx_deepest] == labels] = False