LATM/AAC: Free previously initialized context on reinit.

Fixes memory leaks which are the result of overwriting already-initialized
MDCT contexts during context reinitialization, e.g. in valgrind
fate-aac-latm_000000001180bc60.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/aacdec.c

@@ -2464,6 +2464,7 @@ static int latm_decode_frame(AVCodecContext *avctx, void *out, int *out_size,
             *out_size = 0;
             return avpkt->size;
         } else {
+            aac_decode_close(avctx);
             if ((err = aac_decode_init(avctx)) < 0)
                 return err;
             latmctx->initialized = 1;