mapbench: initialize barrier first
mapbench: initialize barrier first

Oops, previous change introduced a race condition..

aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6