Detect audio loading errors and signal them

[aabounegm]

In the play screen, if a message has an audio whose URL is invalid (or doesn't load for any reason), it shows the user non-functional audio player controls (the play button with the seek bar).
Instead, what should happen is either:

• Hide the audio player controls until it is actually ready to play without errors, or
• Detect audio loading errors and display an error somehow (toast message, disabled controls, red background for the controls, or some combination of those)

It has also been reported by one tester that the automatic audio playback is undesirable, but that's debatable.