Skip poisoned regions

Poisoned regions cannot be accessed without unpoisoning outside gc.c.
Specifically, debug.gem is terminated by AddressSanitizer.

```
SUMMARY: AddressSanitizer: use-after-poison iseq_collector.c:39 in iseq_i
```

1 files changed, 2 insertions, 1 deletions

diff --git a/gc.c b/gc.c
index df4c99b15b..ecb4aa7e20 100644
--- a/gc.c
+++ b/gc.c
@@ -3904,7 +3904,8 @@ objspace_each_objects_try(VALUE arg)
             uintptr_t pstart = (uintptr_t)page->start;
             uintptr_t pend = pstart + (page->total_slots * size_pool->slot_size);
 
-            if ((*data->callback)((void *)pstart, (void *)pend, size_pool->slot_size, data->data)) {
+            if (!__asan_region_is_poisoned((void *)pstart, pend - pstart) &&
+                (*data->callback)((void *)pstart, (void *)pend, size_pool->slot_size, data->data)) {
                 break;
             }