fuzz: Add CScriptNum::getint coverage

src/test/fuzz/scriptnum_ops.cpp

@@ -128,6 +128,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
             script_num &= fuzzed_data_provider.ConsumeIntegral<int64_t>();
             break;
         }
+        (void)script_num.getint();
         // Avoid negation failure:
         // script/script.h:332:35: runtime error: negation of -9223372036854775808 cannot be represented in type 'int64_t' (aka 'long'); cast to an unsigned type to negate this value to itself
         if (script_num != CScriptNum{std::numeric_limits<int64_t>::min()}) {