Proxy: escape explicit space in URI in default cache key.

If the flag space_in_uri is set, the URI in HTTP upstream request is escaped to
convert space to %20.  However this flag is not checked while creating the
default cache key.  This leads to different cache keys for requests
'/foo bar' and '/foo%20bar', while the upstream requests are identical.

Additionally, the change fixes background cache updates when the client URI
contains unescaped space.  Default cache key in a subrequest is always based on
escaped URI, while the main request may not escape it.  As a result, background
cache update subrequest may update a different cache entry.

src/http/modules/ngx_http_proxy_module.c

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index 6bbbfae..efb4bed 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -1095,7 +1095,7 @@
 
     loc_len = (r->valid_location && ctx->vars.uri.len) ? plcf->location.len : 0;
 
-    if (r->quoted_uri || r->internal) {
+    if (r->quoted_uri || r->space_in_uri || r->internal) {
         escape = 2 * ngx_escape_uri(NULL, r->uri.data + loc_len,
                                     r->uri.len - loc_len, NGX_ESCAPE_URI);
     } else {