contrib/plugins/hotblocks: Fix off by one error in iteration of sorted blocks

The logic to iterate over the hottest blocks will never reach the last
item in the list, as it checks `it->next != NULL` before entering the
loop. It's hard to trigger this off-by-one error with the default
limit=20, but it is a bug and is problematic if that default is changed
to something larger.

Signed-off-by: Alex Bradbury <asb@igalia.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Link: https://lore.kernel.org/qemu-devel/f1ba2e57c6126472c0c8310774009f2455efc370.1753857212.git.asb@igalia.com
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

contrib/plugins/hotblocks.c

@@ -82,10 +82,9 @@ static void plugin_exit(qemu_plugin_id_t id, void *p)
     sorted_counts = g_list_sort_with_data(counts, cmp_exec_count, NULL);
 
     if (sorted_counts) {
-        it = sorted_counts;
         g_string_append_printf(report, "pc, tcount, icount, ecount\n");
 
-        for (i = 0; i < limit && it->next; i++, it = it->next) {
+        for (i = 0, it = sorted_counts; i < limit && it; i++, it = it->next) {
             ExecCount *rec = (ExecCount *) it->data;
             g_string_append_printf(
                 report, "0x%016"PRIx64", %d, %ld, %"PRId64"\n",