Close file descriptor after reading "/proc/sys/vm/overcommit_memory".
Close file descriptor after reading "/proc/sys/vm/overcommit_memory".

This bug was introduced by c2f970c32b527660a33fa513a76d913c812dcf7c
(Modify pages_map() to support mapping uncommitted virtual memory.).

This resolves #399.

8l/jemalloc,wqfish/jemalloc,wqfish/jemalloc,8l/jemalloc,wqfish/jemalloc,wqfish/jemalloc,8l/jemalloc,wqfish/jemalloc,8l/jemalloc