Add zero-collocations hack to convert_cvi_colloc

convert_cvi_colloc.py

 
+import os
+import shutil
 import sys
 import numpy as np
 from pyhdf import SD
@@ -8,6 +10,11 @@ class ConvertCviColloc(object):
     def main(self):
 
         colloc_file, out_file = sys.argv[1:]
+        if not os.stat(colloc_file).st_size:
+            print 'Zero collocations'
+            empty_file = os.path.join(os.path.dirname(__file__), 'cris_viiri.empty.hdf')
+            shutil.copy(empty_file, out_file)
+            sys.exit(0)
         explicit_idxs = ExplicitCollocationIndexSet.from_file(
                             colloc_file,
                             ['Master_Index_3', 'Master_Index_2', 'Master_Index_1'],