Guard against the possibility that the queue is emptied while we're iterating
over it. Simple test case:
#include "ngx-queue.h"
#include <assert.h>
int main(void) {
ngx_queue_t h;
ngx_queue_t v[2];
ngx_queue_t* q;
unsigned n = 0;
ngx_queue_init(&h);
ngx_queue_insert_tail(&h, v + 0);
ngx_queue_insert_tail(&h, v + 1);
ngx_queue_foreach(q, &h) {
ngx_queue_remove(v + 0);
ngx_queue_remove(v + 1);
n++;
}
assert(n == 1); // *not* 2
return 0;
}
Fixes#605.
