Fixed If-Range with unknown last modified time.

If modification time isn't known, skip range processing and return full
entity body instead of just ignoring If-Range.  Ignoring If-Range isn't
safe as client will assume entity wasn't changed since time specified.

src/http/modules/ngx_http_range_filter_module.c

diff --git a/src/http/modules/ngx_http_range_filter_module.c b/src/http/modules/ngx_http_range_filter_module.c
index 0eaeff9..329f83d 100644
--- a/src/http/modules/ngx_http_range_filter_module.c
+++ b/src/http/modules/ngx_http_range_filter_module.c
@@ -174,7 +174,11 @@
         goto next_filter;
     }
 
-    if (r->headers_in.if_range && r->headers_out.last_modified_time != -1) {
+    if (r->headers_in.if_range) {
+
+        if (r->headers_out.last_modified_time == (time_t) -1) {
+            goto next_filter;
+        }
 
         if_range = ngx_http_parse_time(r->headers_in.if_range->value.data,
                                        r->headers_in.if_range->value.len);