[libvpx] Update to v1.12.0

libs/libvpx/vp8/decoder/dboolhuff.c

@@ -15,7 +15,13 @@
 int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,
                        unsigned int source_sz, vpx_decrypt_cb decrypt_cb,
                        void *decrypt_state) {
-  br->user_buffer_end = source + source_sz;
+  if (source_sz && !source) return 1;
+
+  // To simplify calling code this fuction can be called with |source| == null
+  // and |source_sz| == 0. This and vp8dx_bool_decoder_fill() are essentially
+  // no-ops in this case.
+  // Work around a ubsan warning with a ternary to avoid adding 0 to null.
+  br->user_buffer_end = source ? source + source_sz : source;
   br->user_buffer = source;
   br->value = 0;
   br->count = -8;
@@ -23,8 +29,6 @@ int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,
   br->decrypt_cb = decrypt_cb;
   br->decrypt_state = decrypt_state;
 
-  if (source_sz && !source) return 1;
-
   /* Populate the buffer */
   vp8dx_bool_decoder_fill(br);