If fallback is enabled, temporarily disable substituters after a failure

Otherwise, we just keep asking the substituter for other .narinfo
files, which can take a very long time due to retries/timeouts.

src/libstore/local-store.cc

@@ -880,6 +880,7 @@ void LocalStore::querySubstitutablePathInfos(const PathSet & paths,
                     narInfo ? narInfo->fileSize : 0,
                     info->narSize};
             } catch (InvalidPath) {
+            } catch (SubstituterDisabled) {
             } catch (Error & e) {
                 if (settings.tryFallback)
                     printError(e.what());