Payment shall not be made out of the state treasury to a witness attending for the Commonwealth in any prosecution for a misdemeanor unless it appears that the sum to which the witness is entitled cannot be obtained:

1. If it be a case wherein there is a prosecutor and the defendant is convicted, by reason of the insolvency of the defendant, or

2. If it be a case in which there is no prosecutor, by reason of the acquittal or insolvency of the defendant or other cause.