fix blank output after exiting confirm via Esc

[midichef]

After exiting a confirm with any of Esc/^C/^Q/q, a status message appears with 5 blank lines.

To test, try to overwrite an existing file: vd sample_data/benchmark.csv press i, ^S Enter and then when the confirm message appears: Esc

The 5 blank lines are produced from the blank Exception: exc(``):

visidata/visidata/form.py

Lines 117 to 119 in c7c83d8

	ret = FormCanvas(source=form).run(vd.scrFull)
	if not ret:
	raise exc('')

That empty string gets turned into vd markup of [:error][/], which is an empty tag. Empty tags are not handled properly by wraptext(). They turn into 5 nearly empty tuples: list(wraptext('[:error][/]')) == [('', ''), ('[:error]', ''), ('', ''), ('[/]', ''), ('', '')], which get turned into 5 blank lines. So I have 1 commit to catch that case. That's needed for correctness in display.

With that fix, hitting Esc after confirm() makes just 1 blank line instead of 5. The second commit then addresses the remaning blank line. It treats Esc/^C/^Q/q the same as presses of n, showing the same disconfirmed: message. Is that intended behavior? Or is Esc intended to produce an escape that can be distinguished from an n?