wmavoice: initialize best_hist_ptr to NULL to prevent (incorrect) warning.

As a sideeffect this makes the code more robust if a future change leaves
a path where it may be uninitialized otherwise.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/wmavoice.c

@@ -515,7 +515,7 @@ static int kalman_smoothen(WMAVoiceContext *s, int pitch,
     float optimal_gain = 0, dot;
     const float *ptr = &in[-FFMAX(s->min_pitch_val, pitch - 3)],
                 *end = &in[-FFMIN(s->max_pitch_val, pitch + 3)],
-                *best_hist_ptr;
+                *best_hist_ptr = NULL;
 
     /* find best fitting point in history */
     do {