Fixes for re-enabling more MSVC level 4 warnings: courgette/ edition

This contains fixes for the following sorts of issues:
* Signedness mismatch

BUG=81439
TEST=none

Review URL: https://codereview.chromium.org/371153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281696 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/courgette/disassembler_elf_32_arm.cc b/courgette/disassembler_elf_32_arm.cc
index dc3712f..f0f94b9 100644
--- a/courgette/disassembler_elf_32_arm.cc
+++ b/courgette/disassembler_elf_32_arm.cc
@@ -215,7 +215,7 @@
     case ARM_OFF21:
       return 4;
     default:
-      return -1;
+      return 0xFFFF;
   }
 }