fix: handle progress for empty files (#3260)

When a file is empty the progress event will have a `Bytes` property
that is `0` so test if the property is not undefined rather than if
it is truthy.

Fixes #3255

Author: achingbrain

src/add-all.js

@@ -32,10 +32,10 @@ module.exports = configure((api) => {
     for await (let file of res.ndjson()) {
       file = toCamel(file)
 
-      if (progressFn && file.bytes) {
-        progressFn(file.bytes)
-      } else {
+      if (file.hash !== undefined) {
         yield toCoreInterface(file)
+      } else if (progressFn) {
+        progressFn(file.bytes || 0)
       }
     }
   }