Fixed HEAD requests handling when proxying is used (closes #261).

src/http/modules/ngx_http_gzip_filter_module.c

diff --git a/src/http/modules/ngx_http_gzip_filter_module.c b/src/http/modules/ngx_http_gzip_filter_module.c
index 470be3d..2f39543 100644
--- a/src/http/modules/ngx_http_gzip_filter_module.c
+++ b/src/http/modules/ngx_http_gzip_filter_module.c
@@ -321,7 +321,7 @@
 
     ctx = ngx_http_get_module_ctx(r, ngx_http_gzip_filter_module);
 
-    if (ctx == NULL || ctx->done) {
+    if (ctx == NULL || ctx->done || r->header_only) {
         return ngx_http_next_body_filter(r, in);
     }
 

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 5e04324..3436c6b 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3099,6 +3099,7 @@
     r->connection->log->action = "sending to client";
 
     if (rc == 0
+        && !r->header_only
 #if (NGX_HTTP_CACHE)
         && !r->cached
 #endif