[mod_webdav] always define webdav_mmap_file_chunk
[mod_webdav] always define webdav_mmap_file_chunk

(previously was defined only if mod_webdav was built with
PROPPATCH and/or LOCK support)

lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4