If a power saver block already exists, do nothing
If a power saver block already exists, do nothing

Before this change, when opening the player, both 'onPlayerOpen' and
'onPlayerPlay' would fire, which enabled, disabled, and re-enabled the
power save blocker in quick succession.

Instead, we just want to activate it once.

feross/webtorrent-desktop,webtorrent/webtorrent-desktop,feross/webtorrent-desktop,yciabaud/webtorrent-desktop,webtorrent/webtorrent-desktop,feross/webtorrent-desktop,webtorrent/webtorrent-desktop,yciabaud/webtorrent-desktop,yciabaud/webtorrent-desktop,michaelgeorgeattard/webtorrent-desktop,michaelgeorgeattard/webtorrent-desktop,feross/webtorrent-app,feross/webtorrent-app,feross/webtorrent-app,michaelgeorgeattard/webtorrent-desktop