Add error handling for all responses in `AppNavi.vue`

[seyfeb]

There are some axios calls in AppNavi.vue which don’t check the response.

We should add some code to check the response and handle any possible errors (this was shortly discussed in #497).

[seyfeb]

Actually, I think they are already checked. The responses fall in the 2xx range; the catch statement handles other codes (compare the axios documentation)

[christianlupus]

I was thinking more of a misconfigured server. If anything goes wrong, NC will most probably return the default page (dashbord it is for my instance currently). So a simple check with the string, if it is OK, might be a good idea.

[christianlupus]

@seyfeb if you think this is a no-issue (maybe in the meantime), you can close this issue as well.

[christianlupus]

See also #577