avcodec/idctdsp: Transmit studio_profile to init instead of using AVCodecContext profile

These 2 fields are not always the same, it is simpler to always use the same field
for detecting studio profile

Fixes: null pointer dereference
Fixes: ffmpeg_crash_3.avi

Found-by: Thuan Pham <thuanpv@comp.nus.edu.sg>, Marcel Böhme, Andrew Santosa and Alexandru RazvanCaciulescu with AFLSmart
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/idctdsp.c

@@ -258,7 +258,7 @@ av_cold void ff_idctdsp_init(IDCTDSPContext *c, AVCodecContext *avctx)
         if (avctx->bits_per_raw_sample == 10 || avctx->bits_per_raw_sample == 9) {
             /* 10-bit MPEG-4 Simple Studio Profile requires a higher precision IDCT
                However, it only uses idct_put */
-            if (avctx->codec_id == AV_CODEC_ID_MPEG4 && avctx->profile == FF_PROFILE_MPEG4_SIMPLE_STUDIO)
+            if (c->mpeg4_studio_profile)
                 c->idct_put              = ff_simple_idct_put_int32_10bit;
             else {
                 c->idct_put              = ff_simple_idct_put_int16_10bit;

libavcodec/idctdsp.h

@@ -95,6 +95,8 @@ typedef struct IDCTDSPContext {
      */
     uint8_t idct_permutation[64];
     enum idct_permutation_type perm_type;
+
+    int mpeg4_studio_profile;
 } IDCTDSPContext;
 
 void ff_put_pixels_clamped_c(const int16_t *block, uint8_t *av_restrict pixels,

libavcodec/mpegvideo.c

@@ -329,6 +329,8 @@ static av_cold int dct_init(MpegEncContext *s)
 
 av_cold void ff_mpv_idct_init(MpegEncContext *s)
 {
+    if (s->codec_id == AV_CODEC_ID_MPEG4)
+        s->idsp.mpeg4_studio_profile = s->studio_profile;
     ff_idctdsp_init(&s->idsp, s->avctx);
 
     /* load & permutate scantables