Prettier formatting when horizontal span is present

[sanxiyn]

Before:

+----+----+-----+
| t1 | t2       |
+====+====+=====+
| a  | bc | def |
+----+----+-----+
|   def   | a   |
+----+----+-----+

After:

+----+----------+
| t1 | t2       |
+====+====+=====+
| a  | bc | def |
+----+----+-----+
|   def   | a   |
+---------+-----+