Panic if TLS fluentd server cannot be connected

[richarticle]

Running below code will panic if fluentd server cannot be connected.

package main

import (
    "github.com/fluent/fluent-logger-golang/fluent"
)

func main() {
    f, _ := fluent.New(fluent.Config{FluentNetwork: "tls", FluentPort: 11111, FluentHost: "127.0.0.1", Async: false})
    f.Post("tag", map[string]string{"log": "msg"})
    f.Post("tag", map[string]string{"log": "msg"})
}

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x59b539]

goroutine 1 [running]:
crypto/tls.(*Conn).SetWriteDeadline(0xc00010baa8?, {0x5f3dd6?, 0x2c?, 0x0?})
        /usr/local/go/src/crypto/tls/conn.go:153 +0x19
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).write.func3(0xc000122000, 0xc0000267b0)
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:606 +0x10e
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).write(0xc000122000, {0x6a8898?, 0xc0000180a8?}, 0xc0000267b0)
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:611 +0xd7
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).writeWithRetry(0xc000122000, {0x6a8898, 0xc0000180a8}, 0xc000026750?)
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:558 +0x5c
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).postRawData(0xc000122000?, 0x644ca5?)
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:300 +0x5b
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).EncodeAndPostData(0x614720?, {0x644ca5?, 0x644c81?}, {0x3?, 0xc0000167f0?, 0x7e7da0?}, {0x614720, 0xc000026750})
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:283 +0xb5
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).PostWithTime(0xc000122000, {0x644ca5?, 0x16365a5d5533203e?}, {0x638f20?, 0x1?, 0x7e7da0?}, {0x614840?, 0xc000026720})
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:274 +0x4ee
github.com/fluent/fluent-logger-golang/fluent.(*Fluent).Post(0x614840?, {0x644ca5, 0x3}, {0x614840, 0xc000026720})
        /home/oliver/go/pkg/mod/github.com/fluent/fluent-logger-golang@v1.9.0/fluent/fluent.go:226 +0x59
main.main()
        /home/oliver/go/projects/test/main.go:9 +0xdc

In Fluent.connect(), below line assigns f.conn a *tls.Conn object instead of net.Conn interface object. Therefore, "f.conn == nil" returns false even if tls.Conn is nil.

f.conn, err = tls.DialWithDialer(