panic: runtime error: index out of range

goroutine 33567 [running]:
gitlab.com/easymarketing/ssh-sender/app/sshMailer.(*LoopStrings).Next(...)
        C:/Users/admin/go/src/gitlab.com/easymarketing/ssh-sender/app/sshMailer/loopstrings.go:22
gitlab.com/easymarketing/ssh-sender/app/sshMailer.CreateMailData(0x1ab02380, 0x17, 0x1a996000, 0x12, 0x82e627a, 0x6, 0x2)
        C:/Users/admin/go/src/gitlab.com/easymarketing/ssh-sender/app/sshMailer/maildata.go:91 +0xa45
main.sendEmailSMTP(0x0, 0x1a996000, 0x12, 0x0, 0x0, 0x0, 0x0, 0x15af, 0x0, 0x1a80e340, ...)
        C:/Users/admin/go/src/SEND/smtps.go:198 +0x20b
created by main.worker
        C:/Users/admin/go/src/SEND/smtps.go:232 +0x139

if ls.index >= len(ls.items) {
    ls.index = 0
}