Merge pull request #21459 from iposva-google/fuzzer-5759629707444224

Fix leak when running b64_decode_fuzzer tests.

test/core/slice/b64_decode_corpus/testcase-5759629707444224

@@ -0,0 +1,6 @@
+=0<EFBFBD>5==0_
+
+
+==0_
+
+==0_==0_

test/core/slice/b64_decode_fuzzer.cc

@@ -27,7 +27,8 @@ bool leak_check = true;
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   if (size < 1) return 0;
   const bool url_safe = static_cast<uint8_t>(0x100) < data[0];
-  grpc_base64_decode_with_len(reinterpret_cast<const char*>(data + 1), size - 1,
-                              url_safe);
+  grpc_slice res = grpc_base64_decode_with_len(
+      reinterpret_cast<const char*>(data + 1), size - 1, url_safe);
+  grpc_slice_unref(res);
   return 0;
 }