replicamanager: Fix NullPointerException

Fixes an NPE when database connection checkout fails:

08 mar 2013 19:56:57 (replicaManager) [] setHeartBeat() ERROR: Can't add/update process 'Adjuster' status in 'heartbeat' table in DB
java.lang.NullPointerException: null
at diskCacheV111.replicaManager.ReplicaDbV1.setHeartBeat(ReplicaDbV1.java:1160) ~[dcache-core-2.6.0-SNAPSHOT.jar:2.6.0-SNAPSHOT]
at diskCacheV111.replicaManager.ReplicaManagerV2$Adjuster.run(ReplicaManagerV2.java:917) [dcache-core-2.6.0-SNAPSHOT.jar:2.6.0-SNAPSHOT]
at dmg.cells.nucleus.CellNucleus$1.run(CellNucleus.java:678) [cells-2.6.0-SNAPSHOT.jar:2.6.0-SNAPSHOT]
at java.lang.Thread.run(Thread.java:722) [na:1.7.0_11]

Target: trunk
Request: 2.5
Request: 2.2
Require-notes: yes
Require-book: no
Patch: http://rb.dcache.org/r/5273/
Committed: master@67d8a291795b6492594543dd16660ccddc89899f
Signed-off-by: Gerd Behrmann <behrmann@nordu.net>