Initialize binary for use as guard later (#3058)

Fixes #3057
diff --git a/test/fuzzers/spvtools_as_fuzzer.cpp b/test/fuzzers/spvtools_as_fuzzer.cpp
index 1b1de00..92aa47f 100644
--- a/test/fuzzers/spvtools_as_fuzzer.cpp
+++ b/test/fuzzers/spvtools_as_fuzzer.cpp
@@ -36,7 +36,7 @@
   input_str.resize(char_count);
   memcpy(input_str.data(), input.data(), input.size() * sizeof(uint32_t));
 
-  spv_binary binary;
+  spv_binary binary = nullptr;
   spv_diagnostic diagnostic = nullptr;
   spvTextToBinaryWithOptions(context, input_str.data(), input_str.size(),
                              SPV_TEXT_TO_BINARY_OPTION_NONE, &binary,