Incompatibility between LowPowerArduino & ArduinoSound

Calling the LowPower.sleep(..) function from the ArduinoLowPower library causes I2S audio playback using the ArduinoSound library to crash.

The sketch below is based on the WavePlayback demo sketch, with a small delay between playbacks. If delay() is used, the sketch works as expected. However, if LowPower.sleep(..) audio playback crashes.

Any ideas or suggestions would be most welcome.

Thank you

```c++
/*
This reads a wave file from an SD card and plays it using the I2S interface to
a MAX08357 I2S Amp Breakout board.

Circuit:
Arduino/Genuino Zero, MKRZero or MKR1000 board
SD breakout or shield connected
MAX08357:
GND connected GND
VIN connected 5V
LRC connected to pin 0 (Zero) or pin 3 (MKR1000, MKRZero)
BCLK connected to pin 1 (Zero) or pin 2 (MKR1000, MKRZero)
DIN connected to pin 9 (Zero) or pin A6 (MKR1000, MKRZero)

created 15 November 2016
by Sandeep Mistry
*/

#include
#include
#include

// filename of wave file to play
const char filename[] = "SONG0.WAV";

// variable representing the Wave File
SDWaveFile waveFile;

void setup() {
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}

// setup the SD card, depending on your shield of breakout board
// you may need to pass a pin number in begin for SS
Serial.print("Initializing SD card...");
if (!SD.begin()) {
Serial.println("initialization failed!");
return;
}
Serial.println("initialization done.");

// create a SDWaveFile
waveFile = SDWaveFile(filename);

// check if the WaveFile is valid
if (!waveFile) {
Serial.println("wave file is invalid!");
while (1); // do nothing
}

// print out some info. about the wave file
Serial.print("Bits per sample = ");
Serial.println(waveFile.bitsPerSample());

long channels = waveFile.channels();
Serial.print("Channels = ");
Serial.println(channels);

long sampleRate = waveFile.sampleRate();
Serial.print("Sample rate = ");
Serial.print(sampleRate);
Serial.println(" Hz");

long duration = waveFile.duration();
Serial.print("Duration = ");
Serial.print(duration);
Serial.println(" seconds");

// adjust the playback volume
AudioOutI2S.volume( 50 );

// check if the I2S output can play the wave file
if (!AudioOutI2S.canPlay(waveFile)) {
Serial.println("unable to play wave file using I2S!");
while (1); // do nothing
}
}

void loop() {
// start playback
Serial.println("starting playback");
AudioOutI2S.play(waveFile);

do {
// wait
}
while ( AudioOutI2S.isPlaying() );

/*
Using delay(..) works as expected
Using LowPower.sleep(..) causes audio playback to stop working
*/

//delay(1000);

LowPower.sleep(1000);

Serial.println("Playing file again ");
AudioOutI2S.play(waveFile);

do {
// wait
}
while ( AudioOutI2S.isPlaying() );

delay(1000);
}
```