Clip negative values before they do any damage.

lib/libvmod_std/vmod_std.c

@@ -230,11 +230,14 @@ VCL_VOID __match_proto__(td_std_cache_req_body)
 vmod_cache_req_body(VRT_CTX, VCL_BYTES size)
 {
 	int result;
+	ssize_t ss;
 
 	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
-	result = VRT_CacheReqBody(ctx, size);
-	VSLb(ctx->vsl, SLT_Debug, "VRT_CacheReqBody(%zu): %d",
-	    (size_t)size, result);
+	if (size < 0)
+		size = 0;
+	ss = (ssize_t)size;
+	result = VRT_CacheReqBody(ctx, ss);
+	VSLb(ctx->vsl, SLT_Debug, "VRT_CacheReqBody(%zd): %d", ss, result);
 }
 
 VCL_STRING __match_proto__(td_std_strstr)