[#1376] Check for null before dereferencing myRescGrpInfo

c1bb19a324ce3e777fc2677bda22ed9b13149e68 fixed a number of leaking
myRescGrpInfo's, but in some cases, matchAndTrimRescGrp() was already
deleting and nulling them, causing seg faults when myRescGrpInfo is
dereferenced to delete rescInfo