Fixed error for missing explict class initialization error on iOS WebRTC buildbots

webrtc/modules/audio_processing/aec3/render_buffer.cc

Index: webrtc/modules/audio_processing/aec3/render_buffer.cc
diff --git a/webrtc/modules/audio_processing/aec3/render_buffer.cc b/webrtc/modules/audio_processing/aec3/render_buffer.cc
index 65dbc8fc2b4610c261e2b35e0246c07ea4e43fb0..a3700dd150228c2bbe53b248545da83f45b0d312 100644
--- a/webrtc/modules/audio_processing/aec3/render_buffer.cc
+++ b/webrtc/modules/audio_processing/aec3/render_buffer.cc
@@ -26,7 +26,8 @@ RenderBuffer::RenderBuffer(Aec3Optimization optimization,
       spectrum_buffer_(num_partitions, std::array<float, kFftLengthBy2Plus1>()),
       spectral_sums_(num_ffts_for_spectral_sums.size(),
                      std::array<float, kFftLengthBy2Plus1>()),
-      last_block_(num_bands, std::vector<float>(kBlockSize, 0.f)) {
+      last_block_(num_bands, std::vector<float>(kBlockSize, 0.f)),
+      fft_() {
   // Current implementation only allows a maximum of one spectral sum lengths.
   RTC_DCHECK_EQ(1, num_ffts_for_spectral_sums.size());
   spectral_sums_length_ = num_ffts_for_spectral_sums[0];