Avoid generating TPM_E_INVALID_HANDLE
Avoid generating TPM_E_INVALID_HANDLE

It looks like in some scenarios the TPM may already have unloaded the key
before we attempt to unload it. Handle that case.

JohnVillalovos/python-tss-1,ph4r05/python-tss,ph4r05/python-tss,JohnVillalovos/python-tss-1,mjg59/python-tss,mjg59/python-tss