Fix leak of data when streaming JPEG

src/JPEGStream.h

@@ -53,7 +53,7 @@ term_closure_destination(j_compress_ptr cinfo){
   closure_destination_mgr *dest = (closure_destination_mgr *) cinfo->dest;
 
   /* emit remaining data */
-  Local<Object> buf = Nan::NewBuffer((char *)dest->buffer, dest->bufsize).ToLocalChecked();
+  Local<Object> buf = Nan::NewBuffer((char *)dest->buffer, dest->bufsize - dest->pub.free_in_buffer).ToLocalChecked();
 
   Local<Value> data_argv[2] = {
       Nan::Null()

test/canvas.test.js

@@ -817,7 +817,7 @@ describe('Canvas', function () {
       bytes += chunk.length;
     });
     stream.on('end', function(){
-      assert.equal(bytes, 8192);
+      assert.equal(bytes, 5427);
       done();
     });
     stream.on('error', function(err) {