avcodec/aacenc: Avoid 0 lambda

Fixes: Ticket8003
Fixes: CVE-2020-20453

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/aacenc.c

@@ -28,6 +28,7 @@
  *              TODOs:
  * add sane pulse detection
  ***********************************/
+#include <float.h>
 
 #include "libavutil/libm.h"
 #include "libavutil/float_dsp.h"
@@ -852,7 +853,7 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
                 /* Not so fast though */
                 ratio = sqrtf(ratio);
             }
-            s->lambda = FFMIN(s->lambda * ratio, 65536.f);
+            s->lambda = av_clipf(s->lambda * ratio, FLT_MIN, 65536.f);
 
             /* Keep iterating if we must reduce and lambda is in the sky */
             if (ratio > 0.9f && ratio < 1.1f) {