Don't panic if return(pass(DURATION)) is used on client side. Ignore

the argument with a VSL message.

Fixes:	#2299

bin/varnishd/cache/cache_vrt.c

@@ -91,6 +91,11 @@ VRT_hit_for_pass(VRT_CTX, VCL_DURATION d)
 	struct objcore *oc;
 
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+	if (ctx->bo == NULL) {
+		VSLb(ctx->vsl, SLT_Error,
+		    "Note: Ignoring DURATION argument to return(pass);");
+		return;
+	}
 	CHECK_OBJ_NOTNULL(ctx->bo, BUSYOBJ_MAGIC);
 	oc = ctx->bo->fetch_objcore;
 	oc->ttl = d;

bin/varnishtest/tests/c00010.vtc

@@ -17,7 +17,7 @@ varnish v1 -vcl+backend {
 		if (req.url == "/foo") {
 			return(hash);
 		} else {
-			return(pass);
+			return(pass(10m));
 		}
 	}
 	sub vcl_hit {