Describe the bug

Decrement (click or btnDown) does not respect "minutes-step" when current val is empty or "00"

Steps to reproduce the bug

<template>
  <div>
    <label for="timepicker-placeholder">Time picker</label>
    <b-form-timepicker id="timepicker-placeholder" minutes-step="15"></b-form-timepicker>
  </div>
</template>

Expected behavior

Also respect minutes-step on decrement from empty or "00".

Versions

Libraries:

• BootstrapVue: 2.6.0
• Bootstrap: 4.4.1
• Vue: 2.6

Environment:

• Device: PC
• OS: Win
• Browser: Firefox
• Version: 73