WaE: comparison of constant 255 with expression of type 'const char'

Better fix for warning: "comparison of constant 255 with expression of
type 'const char' is always true". I hadn't considered that the code
is in a template, so it must handle strings of arbitrary integer types
(well, Unicode).

Change-Id: I38d6d480bfc3ff89db1276cac38d310ecdcc2cfa