Fix unnecessary check in DecimalType
Fix unnecessary check in DecimalType

see https://github.com/doctrine/doctrine2/pull/1104#issuecomment-51755834
v-bartusevicius/dbal,BenMorel/dbal,stchr/dbal,vortgo/dbal,deeky666/dbal,drieschel/dbal,Tobion/dbal,stof/dbal,mikeSimonson/dbal,v-bartusevicius/dbal,gencer/dbal,Tobion/dbal,stchr/dbal,vutung2311/dbal,lcobucci/dbal,vortgo/dbal,lcobucci/dbal,stof/dbal,doctrine/dbal,kimhemsoe/dbal,vutung2311/dbal,doctrine/dbal,BenMorel/dbal,kimhemsoe/dbal,deeky666/dbal,gencer/dbal,mikeSimonson/dbal,drieschel/dbal