Fix line breaks after 'warn' as separate entry.
Fix line breaks after 'warn' as separate entry.

`Kernel.warn` (like `puts`) calls `$stdout.write` twice. For warnings,
the these two were not filtered, causing an extra empty warning in the
console output.

Aerilius/sketchup-console-plus,Aerilius/sketchup-console-plus,Aerilius/sketchup-console-plus