Fix aliasing mimes

[dan-r]

A re-implementation of #1456 as that seems to have been abandoned. This issue mainly affects the use of ariariselseng/camerarawpreviews.

Fixes #1450 and ariselseng/camerarawpreviews#99.

I haven't noticed any regressions when testing this on my local environment and don't see any reason to not change the instantiation of this.currentFile to use this.components[mime] instead of handler.component. This is the approach already used for this.nextFile and this.previousFile.

This also fixes a regression in Viewer.js, allowing no mimes (only aliases) to be provided to registerHandler.

[kesselb]

Are you sure that it does not break the overrideHandlerId feature?

[dan-r]

@kesselb I'm not too familiar with that feature. It looks like it could break that, but in that case I'm not convinced it was working correctly to start with.

The assignments of nextFile and previousFile use this.components[mime] anyway so the initial file you click on would work with the overrideHandlerId function but if you go to the next file, it wouldn't work?

[skjnldsv]

@DaphneMuller this creates other issues, so it's staled until we have proper planning to resolve those issues.

[ariselseng]

@skjnldsv My app camerarawpreviews has been broken due to this since at least Nextcloud 24. It would be great to get this merged/resolved soon. If you browse the issues at camerarawpreviews github repo there is a few duplicate issues every now and then about this.

[skjnldsv]

@ariselseng merging this reverts another bug

I am stuck on this, and don't know what to do