MemoryIntArray: don't double close.

Oops, in the process of trying to track down a double close, I
introduced one...

This was caught by fdsan immediately when running the tests, but a
tombstone wasn't generated, due to a race with ActivityManager killing
crash_dump before it finished generating a tombstone. (b/112564871)

Bug: http://b/112405224
Test: atest MemoryIntArrayTest (looking at logcat this time...)
Change-Id: Iac154b92a945ce9ac8d0721e7bf200e73e6fb484