swr: check channel layouts before using them.

Fixes out of array accesses

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/swresample.c

@@ -265,6 +265,16 @@ av_cold int swr_init(struct SwrContext *s){
         return AVERROR(EINVAL);
     }
 
+    if(av_get_channel_layout_nb_channels(s-> in_ch_layout) > SWR_CH_MAX) {
+        av_log(s, AV_LOG_WARNING, "Input channel layout 0x%"PRIx64" is invalid or unsupported.\n", s-> in_ch_layout);
+        s->in_ch_layout = 0;
+    }
+
+    if(av_get_channel_layout_nb_channels(s->out_ch_layout) > SWR_CH_MAX) {
+        av_log(s, AV_LOG_WARNING, "Output channel layout 0x%"PRIx64" is invalid or unsupported.\n", s->out_ch_layout);
+        s->out_ch_layout = 0;
+    }
+
     switch(s->engine){
 #if CONFIG_LIBSOXR
         extern struct Resampler const soxr_resampler;