Emperfect code around vbucket state on commands

There is currently a hole where a vbucket that transitions between a pending state and another state after the pending state check in a given command which leads the command to thinking that it can proceed even though the vbucket changes state.

Of course, the vbucket can continue to change state at any point throughout this request, so this is not a fatal condition.

RCPtr<VBucket> vb = getVBucket(vbucket);
if (!vb || vb->getState() == dead)

{ return GetValue(ENGINE_NOT_MY_VBUCKET); } else if (vb->getState() == active) { // OK } else if(vb->getState() == replica) { return GetValue(ENGINE_NOT_MY_VBUCKET); }

else if(vb->getState() == pending) {

// bug is in on this line of code

if (vb->addPendingOp(cookie))

{ return GetValue(ENGINE_EWOULDBLOCK); }

}