[mod_webdav] fix crash when plugin_ctx cleaned up (fixes #2780)
[mod_webdav] fix crash when plugin_ctx cleaned up (fixes #2780)

fixes error trace
  (connections.c.273) missing cleanup in webdav

(thx nickrickard)

x-ref:
  "mod_webdav crash with keep-alive (1.4.44)"
  https://redmine.lighttpd.net/issues/2780

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,PatchyFog/lighttpd1.4-mbedtls,PatchyFog/lighttpd1.4-mbedtls,gstrauss/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,PatchyFog/lighttpd1.4-mbedtls