util: Return empty vector on invalid hex encoding

src/util/strencodings.h

@@ -57,9 +57,15 @@ enum class ByteUnit : uint64_t {
 * @return           A new string without unsafe chars
 */
 std::string SanitizeString(std::string_view str, int rule = SAFE_CHARS_DEFAULT);
-/** Parse the hex string into bytes (uint8_t or std::byte). Ignores whitespace. */
+/** Parse the hex string into bytes (uint8_t or std::byte). Ignores whitespace. Returns nullopt on invalid input. */
+template <typename Byte = std::byte>
+std::optional<std::vector<Byte>> TryParseHex(std::string_view str);
+/** Like TryParseHex, but returns an empty vector on invalid input. */
 template <typename Byte = uint8_t>
-std::vector<Byte> ParseHex(std::string_view str);
+std::vector<Byte> ParseHex(std::string_view hex_str)
+{
+    return TryParseHex<Byte>(hex_str).value_or(std::vector<Byte>{});
+}
 signed char HexDigit(char c);
 /* Returns true if each character in str is a hex character, and has an even
  * number of hex digits.*/