Fix regression caused by ee2e9f5

‘basicDrv.inputSrcs’ also contains the outputs of inputDrvs. These
don't necessarily exist in the local store, so copying them may cause
an exception. We should only copy the real inputSrcs.

src/hydra-queue-runner/build-remote.cc

@@ -202,7 +202,7 @@ void State::buildRemote(ref<Store> destStore,
            a no-op for regular stores, but for the binary cache store,
            this will copy the inputs to the binary cache from the local
            store. */
-        copyClosure(ref<Store>(localStore), destStore, basicDrv.inputSrcs);
+        copyClosure(ref<Store>(localStore), destStore, step->drv.inputSrcs);
 
         /* Copy the input closure. */
         if (/* machine->sshName != "localhost" */ true) {