Disposing component without closing throws an error

[nerdoza]

Describe the bug
When the select component is disposed with the select drawer open, an Uncaught TypeError is thrown.

Steps to reproduce the behavior:

1. Add modal or other disposable component with a vue-next-select component nested inside.
2. Open the select draw.
3. Dispose of the parent component without closing the select draw.

Expected behavior
There should be no error thrown.

Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Problem seems to be related to the wrapper ref value being called on line 342 being null.
https://github.com/iendeavor/vue-next-select/blob/9fe934b12c684766093aa2239c48e8b0870969d9/src/index.vue#L341-L349