CLEANUP: Replace for loop with only a condition by while

Refactoring performed with the following Coccinelle patch:

    @@
    expression e;
    statement S;
    @@

    - for (;e;)
    + while (e)
      S
diff --git a/src/h2.c b/src/h2.c
index 84aa660..9ff3c93 100644
--- a/src/h2.c
+++ b/src/h2.c
@@ -535,7 +535,7 @@
 		 * insert "; " before the new value.
 		 */
 		fs += tl; // first one is already counted
-		for (; (ck = list[ck].n.len) >= 0 ; ) {
+		while ((ck = list[ck].n.len) >= 0) {
 			vl = list[ck].v.len;
 			tl += vl + 2;
 			if (tl > fs)