IMPALA-1272: fix crash when compression codec is invalid for parquet

Defer resizing the columns_ vector until we are sure we will initialize it.
Downstream code doesn't expect any NULLs.

Change-Id: I250cceee5181428fcd3cd1a8b021edb7187ae888
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4465
Reviewed-by: Daniel Hecht <dhecht@cloudera.com>
Tested-by: jenkins