Fix CompoundPredicate::CodegenComputeFn
Fix CompoundPredicate::CodegenComputeFn

The codegen'd function was returning false instead of NULL

Change-Id: I481b5b82e3336a71c2a55a7be326af8d39a4d510
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4394
Tested-by: jenkins
Reviewed-by: Nong Li <99a5e5f8f5911755b88e0b536d46aafa102bed41@cloudera.com>

michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala