[MM] Segmentation fault on calling CAPI APIs during destruction

[MM] Segmentation fault on calling CAPI APIs during destruction

Set |player_| as 0 to prevent using invalid handler.

|PlayerPrepared| callback which is set in |player_prepare_async| is called
after calling |Destroy| but it's invalid call path.
To unset remained callbacks, calling the |player_unprepare| in |Destroy|.
|player_unprepare| unset the callback which is set from |player_prepare_async|
and |player_set_position| api.

original M42 patches:
http://165.213.202.130/gerrit/#/c/87061/
http://165.213.202.130/gerrit/#/c/87220/

Bug: http://168.219.209.56/jira/browse/TSAM-379

Reviewed by: sns.park

Change-Id: I37cb9d4955acb12b0c40c5fa5d5ff12cc199d818
Signed-off-by: sangdeug.kim <sangdeug.kim@samsung.com>