tools/target_dem_fuzzer: use avio_context_free() to free the fuzzer's AVIOContext

The doxy for avio_alloc_context() states it must be used for this.

Signed-off-by: James Almer <jamrial@gmail.com>

tools/target_dem_fuzzer.c

@@ -202,7 +202,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     }
 end:
     av_freep(&fuzzed_pb->buffer);
-    av_freep(&fuzzed_pb);
+    avio_context_free(&fuzzed_pb);
     avformat_close_input(&avfmt);
 
     return 0;