xbps_transaction_commit: return error if downloading binpkg/signature fails.
xbps_transaction_commit: return error if downloading binpkg/signature fails.

datenwolf/xbps,datenwolf/xbps,ebfe/xbps,datenwolf/xbps,stpx/xbps,stpx/xbps,ebfe/xbps,stpx/xbps,ebfe/xbps