check it in eden or tomb.

is_pointer_to_heap() checks if it is in valid pointer to the
RVALUE in any heap_page_body. However, it returns true if it
points tomb pages. This patch check it points to eden pages.

gc.c

@@ -2207,8 +2207,10 @@ is_pointer_to_heap(rb_objspace_t *objspace, void *ptr)
 	page = heap_pages_sorted[mid];
 	if (page->start <= p) {
 	    if (p < page->start + page->total_slots) {
-                RB_DEBUG_COUNTER_INC(gc_isptr_maybe);
-		return TRUE;
+                if (!page->flags.in_tomb) {
+                    RB_DEBUG_COUNTER_INC(gc_isptr_maybe);
+                    return TRUE;
+                }
 	    }
 	    lo = mid + 1;
 	}