[indexeddbstorage] Fix putAttachment for empty blob

/reviewed-on nexedi/jio!74

src/jio.storage/indexeddbstorage.js

@@ -385,7 +385,9 @@
               end_index -= 1;
             }
             function resolver(result) {
+              if (result.blob !== undefined) {
                 result_list.push(result);
+              }
               resolve(result_list);
             }
             function getPart(i) {

test/jio.storage/indexeddbstorage.tests.js

@@ -1357,6 +1357,33 @@
       });
   });
 
+  test("retrieve empty blob", function () {
+    var context = this,
+      attachment = "attachment",
+      blob = new Blob();
+    stop();
+    expect(1);
+
+    deleteIndexedDB(context.jio)
+      .then(function () {
+        return context.jio.put("foo", {"title": "bar"});
+      })
+      .then(function () {
+        return context.jio.putAttachment("foo", attachment, blob);
+      })
+      .then(function () {
+        return context.jio.getAttachment("foo", attachment);
+      })
+      .then(function (result) {
+        deepEqual(result, blob, "check empty blob");
+      })
+      .fail(function (error) {
+        ok(false, error);
+      })
+      .always(function () {
+        start();
+      });
+  });
   /////////////////////////////////////////////////////////////////
   // indexeddbStorage.removeAttachment
   /////////////////////////////////////////////////////////////////