fix astanin#365 - exception on empty data with maxheadercolwidths option

Consistency between `maxcolwidths` and `maxheadercolwidths`.

Author: DimitriPapadopoulos

tabulate/__init__.py

@@ -2262,7 +2262,10 @@ def tabulate(
         )
 
     if maxheadercolwidths is not None:
-        num_cols = len(list_of_lists[0])
+        if len(list_of_lists):
+            num_cols = len(list_of_lists[0])
+        else:
+            num_cols = 0
         if isinstance(maxheadercolwidths, int):  # Expand scalar for all columns
             maxheadercolwidths = _expand_iterable(
                 maxheadercolwidths, num_cols, maxheadercolwidths

test/test_regression.py

@@ -515,6 +515,12 @@ def test_exception_on_empty_data_with_maxcolwidths():
     assert_equal(result, "")
 
 
+def test_exception_on_empty_data_with_maxheadercolwidths():
+    "Regression: exception on empty data when using maxheadercolwidths (github issue #365)"
+    result = tabulate([], maxheadercolwidths=5)
+    assert_equal(result, "")
+
+
 def test_numpy_int64_as_integer():
     "Regression: format numpy.int64 as integer (github issue #18)"
     try: