main/app: Fix leaks.

* ast_linear_stream would leak a file descriptor if it failed to allocate
  lin.
* ast_control_tone leaked zone and ts if ast_playtones_start failed.

Additionally added whitespace to ast_linear_stream, pulled assignments
out of conditionals for improved readability.

Change-Id: I6d1a10cf9161b1529d939b9b2d63ea36d395b657