Pass correct frame size for passthrough playback

When estimating the AudioTrack min buffer size, we must use a PCM
frame of 1 when doing direct playback (passthrough). The code was
passing -1 (C.LENGTH_UNSET).

PiperOrigin-RevId: 489238392
(cherry picked from commit d9d716869b)

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -779,7 +779,7 @@ public final class DefaultAudioSink implements AudioSink {
                 getAudioTrackMinBufferSize(outputSampleRate, outputChannelConfig, outputEncoding),
                 outputEncoding,
                 outputMode,
-                outputPcmFrameSize,
+                outputPcmFrameSize != C.LENGTH_UNSET ? outputPcmFrameSize : 1,
                 outputSampleRate,
                 enableAudioTrackPlaybackParams ? MAX_PLAYBACK_SPEED : DEFAULT_PLAYBACK_SPEED);