Fix signed integer overflow in video codec tester

Bug: webrtc:14852
Change-Id: Ia8d704008fe63c7ab28d9ab5a62a396686a1d289
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/475440
Reviewed-by: Jeremy Leconte <jleconte@google.com>
Auto-Submit: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#47790}

test/video_codec_tester.cc

diff --git a/test/video_codec_tester.cc b/test/video_codec_tester.cc
index 0d682ac..a2e9439 100644
--- a/test/video_codec_tester.cc
+++ b/test/video_codec_tester.cc
@@ -651,7 +651,7 @@
             StatsSample(frame.target_bitrate->kbps<double>(), time));
         int buffer_level_bits = leaky_bucket.Update(frame);
         stream.buffer_delay_ms.AddSample(StatsSample(
-            1000 * buffer_level_bits / frame.target_bitrate->bps<double>(),
+            1000.0 * buffer_level_bits / frame.target_bitrate->bps<double>(),
             time));
       }
     }