FIX: Correctly write .annot files with duplicate labels

Author: effigies

nibabel/freesurfer/io.py

@@ -561,7 +561,7 @@ def write_string(s):
         write(-2)
 
         # maxstruc
-        write(np.max(labels) + 1)
+        write(max(np.max(labels) + 1, ctab.shape[0]))
 
         # File of LUT is unknown.
         write_string('NOFILE')

nibabel/freesurfer/tests/test_io.py

@@ -359,7 +359,7 @@ def test_label():
 
 
 def test_write_annot_maxstruct():
-    """Verify we can write files with repeated labels - test by reading"""
+    """Test writing ANNOT files with repeated labels"""
     with InTemporaryDirectory():
         nlabels = 3
         names = ['label {}'.format(l) for l in range(1, nlabels + 1)]