Fix blockstore source end

.travis.yml

@@ -1,9 +1,15 @@
 sudo: false
 language: node_js
-node_js:
-  - 4
-  - 6
-  - stable
+matrix:
+  include:
+  - node_js: 4
+    env: CXX=g++-4.8
+  - node_js: 6
+    env:
+      - SAUCE=true
+      - CXX=g++-4.8
+  - node_js: stable
+    env: CXX=g++-4.8
 
 # Make sure we have new NPM.
 before_install:
@@ -14,12 +20,17 @@ script:
   - npm test
   - npm run coverage
 
-addons:
-  firefox: 'latest'
-
 before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
 
 after_success:
   - npm run coverage-publish
+
+addons:
+  firefox: 'latest'
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-4.8

src/stores/blockstore.js

@@ -123,15 +123,17 @@ exports.setUp = (basePath, BlobStore, locks) => {
       const source = (end, cb) => {
         if (end) {
           ended = end
-        }
-        if (ended) {
-          return cb(ended)
+          return cb(end)
         }
 
         if (written.length) {
           return cb(null, written.shift())
         }
 
+        if (ended) {
+          return cb(ended)
+        }
+
         push = cb
       }