Fix various linter errors

src/backupformat/rsync.js

@@ -47,7 +47,7 @@ async function addFile(sourceFile, encryption, uploader, progressCallback) {
     const hash = new HashStream();
     const destStream = uploader.createStream();
 
-    let pipeline = null;
+    let pipeline;
     if (encryption) {
         const encryptStream = new EncryptStream(encryption);
         pipeline = safe(stream.pipeline(sourceStream, encryptStream, ps, hash, destStream));

src/backupformat/tgz.js

@@ -152,7 +152,7 @@ async function tarPack(dataLayout, encryption, uploader, progressCallback) {
     const hash = new HashStream();
     const destStream = uploader.createStream();
 
-    let pipeline = null;
+    let pipeline;
     if (encryption) {
         const encryptStream = new EncryptStream(encryption);
         pipeline = safe(stream.pipeline(pack, gzip, encryptStream, ps, hash, destStream));