fix static analyzer warnings found by clang analyzer

Author: sleepybishop

src/celt_lpc.c

@@ -208,7 +208,7 @@ int _celt_autocorr(
                    int          n)
 {
    opus_val32 d;
-   int i, k;
+   int i = 0, k = 0;
    int fastN=n-lag;
    int shift;
    const opus_val16 *xptr;

src/kiss_fft.c

@@ -447,7 +447,7 @@ kiss_fft_state *opus_fft_alloc_twiddles(int nfft,void * mem,size_t * lenmem,
     if (st) {
         opus_int16 *bitrev;
         kiss_twiddle_cpx *twiddles;
-
+        memset(st, 0, sizeof(kiss_fft_state));        
         st->nfft=nfft;
 #ifdef FIXED_POINT
         st->scale_shift = celt_ilog2(st->nfft);

src/rnn.c

@@ -162,6 +162,8 @@ void compute_rnn(RNNState *rnn, float *gains, float *vad, const float *input) {
   float dense_out[MAX_NEURONS];
   float noise_input[MAX_NEURONS*3];
   float denoise_input[MAX_NEURONS*3];
+
+  memset(dense_out, 0, sizeof(dense_out));
   compute_dense(rnn->model->input_dense, dense_out, input);
   compute_gru(rnn->model->vad_gru, rnn->vad_gru_state, dense_out);
   compute_dense(rnn->model->vad_output, vad, rnn->vad_gru_state);