update get attachment

Author: stockulus

packages/pouchdb-adapter-asyncstorage/src/get_attachment.js

@@ -16,14 +16,26 @@ export default function (db, docId, attachId, attachment, opts, callback) {
     if (!data || !data.data) {
       return callback(null,
         opts.binary
-          ? global.Buffer.alloc(0, null, type)
+          ? getEmptyBuffer(type)
           : '')
     }
 
     callback(null,
       opts.binary
-        ? global.Buffer.from(data.data, 'base64')
+        ? getBuffer(data.data, type)
         : data.data
     )
   })
 }
+
+const getEmptyBuffer = type => {
+  const buffer = global.Buffer.alloc(0, null, type)
+  buffer.type = type
+  return buffer
+}
+
+const getBuffer = (base64Data, type) => {
+  const buffer = global.Buffer.from(base64Data, 'base64')
+  buffer.type = type
+  return buffer
+}