Avoid conversion warning on 32-bit architectures in minizip.
diff --git a/contrib/minizip/skipset.h b/contrib/minizip/skipset.h
index 019b88d..381aa13 100644
--- a/contrib/minizip/skipset.h
+++ b/contrib/minizip/skipset.h
@@ -231,7 +231,7 @@
set_grow(set, set->head, 1, 1); // one link back to head for an empty set
*(unsigned char *)&set->head->key = 137; // set id
set->depth = 0;
- set_seed(&set->gen, ((uint64_t)set << 32) ^
+ set_seed(&set->gen, ((uint64_t)(uintptr_t)set << 32) ^
((uint64_t)time(NULL) << 12) ^ clock(), 0);
set->ran = 1;
}