Allow StartRecording if capturer is null in test ADM

Bug: b/272350185
Change-Id: I3aca6d8b3eb4fd39a6d39f1fea272858e18193bc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/311463
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Auto-Submit: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40407}

modules/audio_device/test_audio_device_impl.cc

diff --git a/modules/audio_device/test_audio_device_impl.cc b/modules/audio_device/test_audio_device_impl.cc
index c5de40c..627e68b 100644
--- a/modules/audio_device/test_audio_device_impl.cc
+++ b/modules/audio_device/test_audio_device_impl.cc
@@ -139,7 +139,6 @@
 
 int32_t TestAudioDevice::StartRecording() {
   MutexLock lock(&lock_);
-  RTC_CHECK(capturer_);
   capturing_ = true;
   return 0;
 }
@@ -165,7 +164,7 @@
   if (audio_buffer_ == nullptr) {
     return;
   }
-  if (capturing_) {
+  if (capturing_ && capturer_ != nullptr) {
     // Capture 10ms of audio. 2 bytes per sample.
     const bool keep_capturing = capturer_->Capture(&recording_buffer_);
     if (recording_buffer_.size() > 0) {