Fixes HTB bug causing excess tokens to appear

This patch fixes a bug in HTB whereby a variable tracking the current
number of token wasn't appropriately updated under some circumstances.

Change-Id: Iecc2c30765b327748515b7df837e2c395e138d64
Signed-off-by: Duarte Nunes <duarte@midokura.com>
Merge "Fixes HTB bug causing excess tokens to appear"