fs: fix ReadStream.pause() emits duplicate data event

Fixes #3258.

lib/fs.js

@@ -1205,8 +1205,9 @@ ReadStream.prototype.resume = function() {
   this.paused = false;
 
   if (this.buffer) {
-    this._emitData(this.buffer);
+    var buffer = this.buffer;
     this.buffer = null;
+    this._emitData(buffer);
   }
 
   // hasn't opened yet.

test/simple/test-fs-read-stream-resume.js

@@ -0,0 +1,51 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+
+var fs = require('fs');
+var path = require('path');
+
+var file = path.join(common.fixturesDir, 'x.txt');
+var data = '';
+var first = true;
+
+var stream = fs.createReadStream(file);
+stream.setEncoding('utf8');
+stream.on('data', function(chunk) {
+  data += chunk;
+  if (first) {
+    first = false;
+    stream.resume();
+  }
+});
+  
+process.nextTick(function() {
+  stream.pause();
+  setTimeout(function() {
+    stream.resume();
+  }, 100);
+});
+
+process.on('exit', function() {
+  assert.equal(data, 'xyz\n');
+});