Use comparison with a string instead of "is" test with a literal
Use comparison with a string instead of "is" test with a literal

Python 3.8 deprecates "is" test with a literal, which leads to runtime
warnings:

urwid/numedit.py:245: SyntaxWarning: "is not" with a literal. Did you mean "!="?
  if default is not None and default is not "":

Signed-off-by: Andrej Shadura <3fe2fd1720211ac6f19ed41a7088067fb072e2ec@collabora.co.uk>

wardi/urwid,urwid/urwid,inducer/urwid,wardi/urwid,urwid/urwid,wardi/urwid,inducer/urwid,urwid/urwid,inducer/urwid