fix flush block in deflate_slow & enable windowBits test

lib/zlib/deflate.js

@@ -743,11 +743,8 @@ function deflate_slow(s, flush) {
       bflush = trees._tr_tally(s, 0, s.window[s.strstart-1]);
 
       if (bflush) {
-        /*** FLUSH_BLOCK(s, 0); ***/
+        /*** FLUSH_BLOCK_ONLY(s, 0) ***/
         flush_block_only(s, false);
-        if (s.strm.avail_out === 0) {
-          return BS_NEED_MORE;
-        }
         /***/
       }
       s.strstart++;

test/deflate.js

@@ -72,7 +72,7 @@ describe('Deflate levels', function () {
 });
 
 
-describe.skip('Deflate windowBits', function () {
+describe('Deflate windowBits', function () {
 
   it('windowBits 15', function(done) {
     testDeflate(zlib.createDeflate, pako.deflate, samples, { windowBits: 15 }, done);