fix(files_sharing): correctly handle error in case of failing share creation

[Antreesy]

• Resolves: #

Summary

When saving share, there's already a try-catch block to handle process and UI changes:

	let share
	try {
		this.creating = true
		share = await this.addShare(incomingShare)
	} catch {
		this.creating = false
		// Error is already handled by ShareRequests mixin
		return
	}

but this.addShare also have a try-catch, and if error happens there, it's not exposed to this.saveShare, and further handling fails.

Steps to reproduce (one of the ways):

• set password policy (always ask for password, e.t.c.)
• input invalid password
• click 'Save share'

Results wih this PR:

• UI is reset, request failed, toast message (invalid password) is shown

Results without this PR:

• UI is stuck in creating state, request failed, saveShare proceed further, share is undefined

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

[Antreesy]

/compile rebase

[Antreesy]

/compile

[Antreesy]

/backport to stable32

[Antreesy]

/backport to stable31