fix typo in parsing extension of out_file for Qwarp

Author: gpiantoni

nipype/interfaces/afni/preprocess.py

@@ -3784,7 +3784,7 @@ def _list_outputs(self):
             prefix = self.inputs.out_file
             ext_ind = max([
                 prefix.lower().rfind('.nii.gz'),
-                prefix.lower().rfind('.nii.')
+                prefix.lower().rfind('.nii')
             ])
             if ext_ind == -1:
                 ext = '.HEAD'