R1:54ee51d7abd0

Work around exception in Herald transcript of old tasks: Call to a member function getAppliedTransactionPHIDs() on bool

Summary:
In some cases, older Herald transcripts which got garbage collected display an exception.
For unknown reasons, calling `getObjectTranscript()` on the HeraldTranscript object `$xscript` can return a bool with the value `false`.
Afterwards, calling `getAppliedTransactionPHIDs()` on that bool throws an exception.
Thus as a workaround, return an empty array instead in this case…