Perl: creating input and error streams if closed.

Application handler can do anything with a stream object (including close it).
Once the stream is closed, Unit creates a new stream.

This closes #616 issue on GitHub.

docs/changes.xml

@@ -31,6 +31,12 @@ NGINX Unit updated to 1.27.0.
          date="" time=""
          packager="Andrei Belov <defan@nginx.com>">
 
+<change type="bugfix">
+<para>
+some Perl applications failed to process the request body, notably with Plack.
+</para>
+</change>
+
 </changes>