Fix memory leak in mod_deflate.c when SetOutputFilter is enabled and DEFLATE

Fix memory leak in mod_deflate.c when SetOutputFilter is enabled and DEFLATE
is the first filter in the chain - this is seen with mod_dav + mod_deflate
when the client can not do gzip and we constantly do the filter checks.

* modules/filters/mod_deflate.c
  (deflate_ctx): Add a flag as to whether we are successfully initialized.
  (deflate_out_filter): Always create filter ctx and set filter_init flag only
  after we are successfully initialized.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1103315 13f79535-47bb-0310-9956-ffa450edef68