Fix zone offset in time parser

[moorereason]

Describe the bug Given 0=0000-01-01 00:00:00+27000, go-toml doesn't return an error on the time zone offset.

$ echo "0=0000-01-01 00:00:00+27000" | gotoml-test-decoder
{
  "0": {
    "type": "datetime",
    "value": "0000-01-01T00:00:00+27:00"
  }
}

To Reproduce https://go.dev/play/p/fES37UrI64-

toml.Unmarshal([]byte("0=0000-01-01 00:00:00+27000"), &v)

Expected behavior I expected to see an error on invalid time zone offset since it has 5 digits instead of the max of 4. Per RFC3339/ISO8601 ABNF:

time-hour         = 2DIGIT ; 00-24
time-minute       = 2DIGIT ; 00-59
time-numoffset    = ("+" / "-") time-hour [[":"] time-minute]

Versions

• go-toml: 4c7a337083984897cf20bd8fcfcf3525b19f4a55
  • go version go1.17.3 linux/amd64

Additional context Found while doing differential fuzzing against toml-dart.

[pelletier]

Should be fixed in https://github.com/pelletier/go-toml/commit/3990899d7eec45790be0f4a5344e387a89098181.