irssi/scrollwarn: use level constant instead of string for warning
irssi/scrollwarn: use level constant instead of string for warning

Reported-by: nico <d659c10e27d52b00987b65e85d99bce5480adcae@lifeisabug.com>

grawity/hacks,grawity/hacks,grawity/hacks,grawity/hacks,grawity/hacks,grawity/hacks,grawity/hacks