BUG/MEDIUM: http-client: Eat output data when waiting for appctx shutdown

When the http-client applet is executed while a shut is pending, the
remaining output data must always be consumed. Otherwise, this can prevent
the stream to exit, leading to a spinning loop on the applet.

It is 2.8-specific. No backport needed.
diff --git a/src/http_client.c b/src/http_client.c
index 29db28f..c2dec8b 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -700,9 +700,14 @@
 	uint32_t sz;
 	int ret;
 
-	if (unlikely(se_fl_test(appctx->sedesc, (SE_FL_EOS|SE_FL_ERROR|SE_FL_SHR|SE_FL_SHW))))
+	if (unlikely(se_fl_test(appctx->sedesc, (SE_FL_EOS|SE_FL_ERROR|SE_FL_SHR|SE_FL_SHW)))) {
+		if (co_data(res)) {
+			htx = htx_from_buf(&res->buf);
+			co_htx_skip(res, htx, co_data(res));
+			htx_to_buf(htx, &res->buf);
+		}
 		goto out;
-
+	}
 	/* The IO handler could be called after the release, so we need to
 	 * check if hc is still there to run the IO handler */
 	if (!hc)