[6.0] 3cd55a65e std.ip: Always provide some form of fallback

[Dridi Boukelmoune]

commit 3cd55a65ec2c58f819d84b61a819a30470796cb3
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Mon Nov 29 16:00:20 2021 +0100

    std.ip: Always provide some form of fallback
    
    Otherwise valid code can panic on workspace exhaustion:
    
        std.ip(req.http.X-Real-IP, std.ip(req.http.X-Client-IP, client.ip))
    
    If the nested std.ip() call runs out of workspace, it will return a null
    ip instead of the fallback, and the outer std.ip() call will panic upon
    checking the suckaddr sanity.
    
    Refs #3746

diff --git a/lib/libvmod_std/vmod_std_conversions.c b/lib/libvmod_std/vmod_std_conversions.c
index 0bfa0ad7f..89fe23160 100644
--- a/lib/libvmod_std/vmod_std_conversions.c
+++ b/lib/libvmod_std/vmod_std_conversions.c
@@ -90,7 +90,7 @@ vmod_ip(VRT_CTX, VCL_STRING s, VCL_IP d, VCL_BOOL n, VCL_STRING default_port)
 	p = WS_Alloc(ctx->ws, vsa_suckaddr_len);
 	if (p == NULL) {
 		VRT_fail(ctx, "std.ip: insufficient workspace");
-		return (NULL);
+		return (d);
 	}
 
 	if (s != NULL)