Fix compilation issue detected by internal tool.

webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc

Index: webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
diff --git a/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc b/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
index 300baf8eb2a3b68c13e8de273eb952603f39f403..740c257b4a927e21a2cadfded0371ffb4ebd439f 100644
--- a/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
+++ b/webrtc/modules/audio_processing/aec3/adaptive_fir_filter.cc
@@ -236,6 +236,7 @@ AdaptiveFirFilter::AdaptiveFirFilter(size_t size_partitions,
                                      Aec3Optimization optimization,
                                      ApmDataDumper* data_dumper)
     : data_dumper_(data_dumper),
+      fft_(),
       optimization_(optimization),
       H_(size_partitions) {
   RTC_DCHECK(data_dumper_);