Use current time as initial timestamp on error

If the initial timestamp could not be retrieved, use the current time as
returned by System.nanoTime(). In practice, it is the same time base as
AudioRecord timestamps.

Fixes #4536 <https://github.com/Genymobile/scrcpy/issues/4536>

server/src/main/java/com/genymobile/scrcpy/AudioCapture.java

@@ -153,7 +153,8 @@ public final class AudioCapture {
             previousRecorderTimestamp = timestamp.nanoTime;
         } else {
             if (nextPts == 0) {
-                Ln.w("Could not get any audio timestamp");
+                Ln.w("Could not get initial audio timestamp");
+                nextPts = System.nanoTime() / 1000;
             }
             // compute from previous timestamp and packet size
             pts = nextPts;