add double null check to asm stub builders

currently the code generated does a null check within the synchronized code. this forces all threads to block while the check is made even after the check returns false. by adding a double null check, the synchronized code is bypassed once the check is satisfied.

public void evaluate(KnowledgeHelper paramKnowledgeHelper, WorkingMemory paramWorkingMemory)
throws Exception
{
if (this.consequence == null) {
synchronized (this) {
if (this.consequence == null)

{ ConsequenceGenerator.generate(this, paramKnowledgeHelper, paramWorkingMemory); }

}
}
this.consequence.evaluate(paramKnowledgeHelper, paramWorkingMemory);
}