Fix for read_head with try_files and open_file_cache.

The of.read_ahead wasn't set in try_files code path, causing read_ahead
directive to be a nop if try_files and open_file_cache were used.

src/http/ngx_http_core_module.c

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index e666823..3c57117 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -1289,6 +1289,7 @@
 
         ngx_memzero(&of, sizeof(ngx_open_file_info_t));
 
+        of.read_ahead = clcf->read_ahead;
         of.directio = clcf->directio;
         of.valid = clcf->open_file_cache_valid;
         of.min_uses = clcf->open_file_cache_min_uses;