Fix overflow testing in sbrk. am: 1944780b62 am: 3a5ebf3154  -s ours am: d95336ac42 am: 0993319651 am: 0ae30d9af8
am: 83b0671a33

* commit '83b0671a33a0da3d0ed962f8f01ff166069093dd':
  Fix overflow testing in sbrk.

Change-Id: Id325431f9de4bdfe102381da21445fa0781ccc82