tools/target_dec_fuzzer: Do not attempt to fuzz VDPAU, its not supported

Fixes: 1364/clusterfuzz-testcase-minimized-6459843441328128
Fixes: 1392

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

tools/target_dec_fuzzer.c

@@ -147,6 +147,10 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         avcodec_register(&DECODER_SYMBOL(FFMPEG_DECODER));
 
         c = &DECODER_SYMBOL(FFMPEG_DECODER);
+
+        // Unsupported
+        if (c->capabilities & AV_CODEC_CAP_HWACCEL_VDPAU)
+            return 0;
 #else
         avcodec_register_all();
         c = AVCodecInitialize(FFMPEG_CODEC);  // Done once.