[master] 2399d524a http: Polish using pdiff() macro

[Dridi Boukelmoune]

commit 2399d524a686eb86e202464dcd02d7e2ce87cd41
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Tue Apr 1 15:21:38 2025 +0200

    http: Polish using pdiff() macro

diff --git a/bin/varnishd/cache/cache_http.c b/bin/varnishd/cache/cache_http.c
index 26ec4d054..31c533f30 100644
--- a/bin/varnishd/cache/cache_http.c
+++ b/bin/varnishd/cache/cache_http.c
@@ -187,9 +187,7 @@ http_hdr_flags(const char *b, const char *e)
 
 	if (b == NULL || e == NULL)
 		return (NULL);
-	assert(b <= e);
-	u = (unsigned)(e - b);
-	assert(b + u == e);
+	u = pdiff(b, e);
 	if (u < GPERF_MIN_WORD_LENGTH || u > GPERF_MAX_WORD_LENGTH)
 		return (NULL);
 	u += http_asso_values[(uint8_t)(e[-1])] +