Resuming a paused sound was not working correctly
due to a guard in Play that prevented the same instance being played twice.
Now also protects against Resume and Pause being called many times.
Fixes issue #1263.
Merge pull request #1292 from slygamer/issue1263

Resuming a paused sound was not working correctly
Merge branch 'develop3d' of https://github.com/mono/MonoGame into develop3d