rpm: opendb before rpmverifyscript to avoid null point input

rpm: opendb before rpmverifyscript to avoid null point input

If the command is "rpm -V" and the return value of (headerIsEntry(h, RPMTAG_VERIFYSCRIPT)
|| headerIsEntry(h, RPMTAG_SANITYCHECK)) located in /lib/verify.c is true, it will call
rpmpsmStage function(rpmVerifyScript->rpmpsmScriptStage->rpmpsmStage) and occur segment
fault because of null point(rpmtsGetRdb(ts) == NULL and rpmtsGetRdb(ts)->db_txn).
So we open rpmdb to avoid bad input when find headerIsEntry true.

workflow:
main()->rpmcliVerify()->rpmcliArgIter()->rpmQueryVerify()->rpmgiShowMatches()->showVerifyPackage()->
          rpmqv.c         verify.c        query.c             query.c           verify.c(headerIsEntry)
rpmVerifyScript()->rpmpsmScriptStage()->rpmpsmStage()->    rpmtxnCommit(rpmtsGetRdb(ts)->db_txn);
      verify.c            psm.c             psm.c                 psm.c

Signed-off-by: Zhixiong Chi <zhixiong.chi@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>