BUG/MINOR: http: Use out buffer instead of trash to display error snapshot

the function http_show_error_snapshot() must not use the trash buffer to append
the HTTP error description. Instead, it must use the <out> buffer, its first
argument. Note that concretely, this function always succeeds because <out> is
always the trash buffer.
diff --git a/src/proto_http.c b/src/proto_http.c
index 7c658d9..43c1fcd 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -7421,7 +7421,7 @@
  */
 void http_show_error_snapshot(struct buffer *out, const struct error_snapshot *es)
 {
-	chunk_appendf(&trash,
+	chunk_appendf(out,
 	              "  stream #%d, stream flags 0x%08x, tx flags 0x%08x\n"
 	              "  HTTP msg state %s(%d), msg flags 0x%08x\n"
 	              "  HTTP chunk len %lld bytes, HTTP body len %lld bytes, channel flags 0x%08x :\n",