Clamp to positive value when computing latency for an output stream

Diagnosed by jolin@mozilla.com, the same code is also found in Chromium.

src/cubeb_aaudio.cpp

@@ -644,8 +644,10 @@ aaudio_get_latency(cubeb_stream * stm, aaudio_direction_t direction,
   // Extrapolate from the known timestamp for a particular frame presented.
   int64_t app_frame_hw_time = hw_tstamp + frame_time_delta;
   // For an output stream, the latency is positive, for an input stream, it's
-  // negative.
+  // negative. It can happen in some instances, e.g. around start of the stream
-  int64_t latency_ns = is_output ? app_frame_hw_time - signed_tstamp_ns
+  // that the latency for output is negative, return 0 in this case.
+  int64_t latency_ns = is_output
+                           ? std::max(0ll, app_frame_hw_time - signed_tstamp_ns)
                            : signed_tstamp_ns - app_frame_hw_time;
   int64_t latency_frames = stm->sample_rate * latency_ns / NS_PER_S;