i#1580 vmareas app_pc potential uninit: Initializes offending vars to NULL
i#1580 vmareas app_pc potential uninit: Initializes offending vars to NULL

Initializes prev_start and next_start to NULL to make the compiler happy.

Fixes #1580

Review-URL: https://codereview.appspot.com/188550043

AmesianX/dynamorio,sigma-random/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,sigma-random/dynamorio,bl4ckic3/dynamorio,sigma-random/dynamorio,sigma-random/dynamorio,code4bones/dynamorio,code4bones/dynamorio,sigma-random/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,daksunt/dynamorio,code4bones/dynamorio,bl4ckic3/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio