plist: Fix assert() to allow 16 or 8 byte integer sizes (16 bytes = unsigned integer)

Credit to Wang Junjie <zhunkibatu@gmail.com> (#90)
Credit to OSS-Fuzz
diff --git a/src/plist.c b/src/plist.c
index 3314378..f62e6be 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -767,7 +767,7 @@
     uint64_t length = 0;
     if (PLIST_UINT == type)
         plist_get_type_and_value(node, &type, (void *) val, &length);
-    assert(length == sizeof(uint64_t));
+    assert(length == sizeof(uint64_t) || length == 16);
 }
 
 PLIST_API void plist_get_uid_val(plist_t node, uint64_t * val)