Do not crash padding an empty table

[eeshsaxena]

pad_tables_in_text crashes with IndexError on an empty table block:

from html2text import config
from html2text.utils import pad_tables_in_text
m = config.TABLE_MARKER_FOR_PAD
pad_tables_in_text(f"{m}\n{m}\n")   # IndexError: list index out of range

When the closing marker is reached the buffered table lines are handed to reformat_table, which reads lines[0] for the column widths. Two markers with nothing between them leave that buffer empty, so it indexes an empty list. Added an early return for the no-lines case, plus a test.

[eeshsaxena]

Hi! Gentle nudge on this one whenever you have some bandwidth. It's a small, self-contained fix (Do not crash padding an empty table), and it's currently mergeable with no conflicts. No urgency at all, and I'm happy to make any changes you'd like. Thanks for maintaining html2text!