BUGFIX Checking for existence of constraint specs to avoid PHP notice errors on schema updates in PotgreSQLDatabase->alterTableAlterColumn() (regression from r113928)
BUGFIX Checking for existence of constraint specs to avoid PHP notice errors on schema updates in PotgreSQLDatabase->alterTableAlterColumn() (regression from r113928)

minhvip20956/SilverstripeHeroku,tractorcow/silverstripe-postgresql