Re-query for the derivation outputs in the post-build-hook

We can't assume that the runtime state knows about them as they might have
been built remotely, in which case we must query the db again to get
them.

src/libstore/build/derivation-goal.cc

@@ -899,8 +899,10 @@ void DerivationGoal::buildDone()
                 Logger::Fields{worker.store.printStorePath(drvPath)});
             PushActivity pact(act.id);
             StorePathSet outputPaths;
-            for (auto i : drv->outputs) {
-                outputPaths.insert(finalOutputs.at(i.first));
+            for (auto& [_, maybeOutPath] :
+                 worker.store.queryPartialDerivationOutputMap(drvPath)) {
+                if (maybeOutPath)
+                    outputPaths.insert(*maybeOutPath);
             }
             std::map<std::string, std::string> hookEnvironment = getEnv();