Fix tautological compare in rlz.

Fix tautological compare in rlz.

This fixes this warning from a recent version of Clang:

  rlz/lib/string_utils.cc:14:35: error: comparison of constant 128 with
  expression of type 'char' is always true
  [-Werror,-Wtautological-constant-out-of-range-compare]
    return (letter >= 0x0 && letter < 0x80);
                                 ~~~~~~ ^ ~~~~

BUG=163104
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=170265

[Nico, 2012-11-29 20:30:54]

lgtm

[commit-bot: I haz the power, 2012-11-29 20:31:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hans@chromium.org/11434029/1

[commit-bot: I haz the power, 2012-11-29 22:51:51]

Change committed as 170265