avcodec/dxv: Initialize tex_funct to NULL

Fixes: Various anomalies
Fixes: 14493/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DXV_fuzzer-5071018000908288
Fixes: 14630/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DXV_fuzzer-5714888963391488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/dxv.c

@@ -1057,6 +1057,10 @@ static int dxv_decode(AVCodecContext *avctx, void *data,
     avctx->pix_fmt = AV_PIX_FMT_RGBA;
     avctx->colorspace = AVCOL_SPC_RGB;
 
+    ctx->tex_funct = NULL;
+    ctx->tex_funct_planar[0] = NULL;
+    ctx->tex_funct_planar[1] = NULL;
+
     tag = bytestream2_get_le32(gbc);
     switch (tag) {
     case MKBETAG('D', 'X', 'T', '1'):