Proxy: simplified conditions of using unparsed uri.

Previously, the unparsed uri was explicitly allowed to be used only by the main
request.  However the valid_unparsed_uri flag is nonzero only in the main
request, which makes the main request check pointless.
diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index b42839c..6bbbfae 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -1086,8 +1086,7 @@
 
         return NGX_OK;
 
-    } else if (ctx->vars.uri.len == 0 && r->valid_unparsed_uri && r == r->main)
-    {
+    } else if (ctx->vars.uri.len == 0 && r->valid_unparsed_uri) {
         *key = r->unparsed_uri;
         u->uri = r->unparsed_uri;
 
@@ -1201,8 +1200,7 @@
     if (plcf->proxy_lengths && ctx->vars.uri.len) {
         uri_len = ctx->vars.uri.len;
 
-    } else if (ctx->vars.uri.len == 0 && r->valid_unparsed_uri && r == r->main)
-    {
+    } else if (ctx->vars.uri.len == 0 && r->valid_unparsed_uri) {
         unparsed_uri = 1;
         uri_len = r->unparsed_uri.len;