Non-digits in time zone offset

[moorereason]

Describe the bug
Time zone offset parser doesn't ensure only digits are used.

To Reproduce
With gotoml-test-decoder:

$ echo "0=0000-01-01 00:00:00+00:0Z" | gotoml-test-decoder
{
  "0": {
    "type": "datetime",
    "value": "0000-01-01T00:00:00+00:42"
  }
}

Test cases:

diff --git a/unmarshaler_test.go b/unmarshaler_test.go
index c29f9ac..d6bd268 100644
--- a/unmarshaler_test.go
+++ b/unmarshaler_test.go
@@ -2632,6 +2632,14 @@ world'`,
                        desc: `invalid number of seconds digits with trailing digit`,
                        data: `a=0000-01-01 00:00:000000Z3`,
                },
+               {
+                       desc: `invalid character in zone offset hours`,
+                       data: `a=0000-01-01 00:00:00+0Z:00`,
+               },
+               {
+                       desc: `invalid character in zone offset minutes`,
+                       data: `a=0000-01-01 00:00:00+00:0Z`,
+               },
                {
                        desc: `invalid number of seconds`,
                        data: `a=0000-01-01 00:00:00+27000`,

Expected behavior
Expected to receive an error.

Versions

• go-toml: c862c34
• go version go1.17.3 linux/amd64

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

[pelletier]

Thought I had completely removed that function that doesn't check errors when parsing digits 😅

[pelletier]

Fixed in 9bf9be6. The offending function is no more.