fix: handle empty tables when maxheadercolwidths is set

[Jo2234]

Summary

Fix IndexError when tabulate() is called with an empty table and maxheadercolwidths is not None.

Problem

from tabulate import tabulate
tabulate([], headers=['Name', 'Age'], maxheadercolwidths=10)
# IndexError: list index out of range

The crash occurs at:

if maxheadercolwidths is not None:
    num_cols = len(list_of_lists[0])  # IndexError when list_of_lists is empty

Fix

 if maxheadercolwidths is not None:
-    num_cols = len(list_of_lists[0])
+    if len(list_of_lists):
+        num_cols = len(list_of_lists[0])
+    elif len(headers):
+        num_cols = len(headers)
+    else:
+        num_cols = 0
+    if num_cols:
         ...  # existing width wrapping logic

This mirrors the approach already used for maxcolwidths (lines 2250-2253) which correctly handles empty tables.

Fixes #365