Too many simultaneous sounds turns off music

[brisbang]

As described in chaosforgeorg/drl#289, and through analysis, playing 128 sounds deactivates the music. Music can be immediately restarted if required.

The desired behaviour appears to be that the sounds are capped at 127 and the music remains on, rather than feeding the player an extra sound at the cost of music.

[brisbang]

The change has been implemented in vfmodsound but not in the base class because:

• the issue could be tied to the specific sound library implementation.
• it's not clear if the methods should be attempted for porting to other sound libraries.

Testing:
A level with 156 adjacent monsters was generated. Logging was turned on for the PlaySound call. Movement back and forth was performed. The logs show the number of times the method was called.
In this case hundreds of calls were made within a second and the music remained operational.

Previously this number of back and forths was enough to generate silence.