Make gzip work with app that is generatorgzip_work_with_generator

```
$ tox
...
  py26: commands succeeded
  py27: commands succeeded
  py34: commands succeeded
  py35: commands succeeded
  pypy: commands succeeded
  congratulations :)
```

1 files changed, 9 insertions, 6 deletions

diff --git a/paste/gzipper.py b/paste/gzipper.py
index eca8775..5f59141 100644
--- a/paste/gzipper.py
+++ b/paste/gzipper.py
@@ -71,15 +71,18 @@ class GzipResponse(object):
         return [s]
 
     def finish_response(self, app_iter):
-        if self.compressible:
-            output = gzip.GzipFile(mode='wb', compresslevel=self.compress_level,
-                fileobj=self.buffer)
-        else:
-            output = self.buffer
+        output = None
+
         try:
             for s in app_iter:
+                if not output:
+                    if self.compressible:
+                        output = gzip.GzipFile(mode='wb', compresslevel=self.compress_level,
+                            fileobj=self.buffer)
+                    else:
+                        output = self.buffer
                 output.write(s)
-            if self.compressible:
+            if output and self.compressible:
                 output.close()
         finally:
             if hasattr(app_iter, 'close'):