Gallery2: Fix crash for unsupported format on mute operation

Mpeg4 Writer does not support formats other than mp4/h264/h263.
Need to check in app for unsupported format before starting mute
operation.
Fix is to add condition in app to check for unsupported format and
display toast message.

Change-Id: I6c3fda284a3eb5e4483c6ec268a1f2c4d79d6773