fstrace: Don't read uninitialised data on other platforms either

Commit 908105fe8d51551e45692de4e145022138a0356c fixed an off-by-one
error potentially causing a buffer overread in CheckTypes, but only
in the IRIX/AIX version of the function. Apply the same fix to the
code for the other platforms.

Spotted by Andrew Deason.

Change-Id: I5f70c072e609337b39064ba48353b4fdf23acf17
Reviewed-on: http://gerrit.openafs.org/11185
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>