Dereference of an explicit null value

Defect 99859 (STATIC_C)
Checker FORWARD_NULL (subcategory deref_constant_null)
File: /src/third_party/wiredtiger/src/btree/bt_read.c
Function __las_page_instantiate
/src/third_party/wiredtiger/src/btree/bt_read.c, line: 136
Assigning: "upd" = "NULL".

    	first_upd = last_upd = upd = NULL;