C: Fix O(n) linked list walk in hb_arena_append_page() (#1380)

This PR changes the way we add pages in the arena allocator, instead of
seeking to the tail page starting from the head, we directly use the
tail page.

Additionally this PR asserts that if the head page is null, the tail
page also should be null.

---------

Co-authored-by: Michael Kohl <me@citizen428.net>

Author: timkaechele

src/util/hb_arena.c

@@ -70,16 +70,12 @@ static bool hb_arena_append_page(hb_arena_T* allocator, size_t page_size) {
   page->position = 0;
 
   if (allocator->head == NULL) {
+    assert(allocator->tail == NULL);
+
     allocator->head = page;
     allocator->tail = page;
   } else {
-    hb_arena_page_T* last = allocator->head;
-
-    while (last->next != NULL) {
-      last = last->next;
-    }
-
-    last->next = page;
+    allocator->tail->next = page;
     allocator->tail = page;
   }