Fix test failure in debug mode on windows
Fix test failure in debug mode on windows

When building under CMAKE_BUILD_TYPE=Debug isupper (with friends)
throw an exception if ii < -1 || > 255. Given that we only allow
a small subset of characters we can just bail out if it's negative.

Change-Id: Icc849f76559904a17ac68c9a7ed61919b5695b4d
Reviewed-on: http://review.couchbase.org/68211
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

couchbase/memcached,couchbase/memcached,daverigby/kv_engine,couchbase/memcached,daverigby/kv_engine,daverigby/kv_engine,daverigby/memcached,daverigby/memcached,couchbase/memcached,daverigby/kv_engine,daverigby/memcached,daverigby/memcached