Added error after adding interval with no note selected

[randoguyname]

Shows an error if the "add interval" function is called when no note or chord is selected. Resolves: #13296

• [x] I signed the CLA
• [x] The title of the PR describes the problem it addresses
• [x] Each commit's message describes its purpose and effects, and references the issue it resolves
• [x] If changes are extensive, there is a sequence of easily reviewable commits
• [x] The code in the PR follows the coding rules
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• [ ] I created a unit test or vtest to verify the changes I made (if applicable)

[DmitryArefiev]

Tested #13296 on Win10

@randoguyname I see the dialog's shape and some text style a little bit different comparing with other dialog. Can you change it to make more similar?

https://user-images.githubusercontent.com/90187801/212703358-c5c80650-e7a1-418a-ba4b-840afe310470.mp4

[cbjeukendrup]

@DmitryArefiev The shape is determined by the width of the text. We could give these message dialogs a minimum width, but I'm not sure if that's in the scope of this PR.

And about the text style, I believe that this new dialog follows the desired design more closely than the one about staff texts.

[DmitryArefiev]

@DmitryArefiev The shape is determined by the width of the text. We could give these message dialogs a minimum width, but I'm not sure if that's in the scope of this PR.

And about the text style, I believe that this new dialog follows the desired design more closely than the one about staff texts.

It just seems to tight for me)

@bkunda @jessjwilliamson Please review

[wizofaus]

I'd be more worried about having "Don't show this again" on a dialog that's the only feedback you get that you've tried to use a command when it doesn't make sense...

[randoguyname]

I'd like to point out that this isn't a new dialog at all, rather an application of the existing no note selected dialog.

[DmitryArefiev]

I'd be more worried about having "Don't show this again" on a dialog that's the only feedback you get that you've tried to use a command when it doesn't make sense...

@wizofaus I think that's fine since the checkbox is not checked by default

[DmitryArefiev]

I'd like to point out that this isn't a new dialog at all, rather an application of the existing no note selected dialog.

@randoguyname Got it. Thanks! I'll create a separate issue for inconsistency in dialog style

[DmitryArefiev]

Tested #13296 on Win10, Mac12, LinuxMint 22.04 - FIXED

[DmitryArefiev]

@cbjeukendrup Should this be rebased and reviewed again? Or we can merge into master now?

[cbjeukendrup]

The change is quite trivial enough and I don't think there have been any potentially conflicting other changes in the meantime, so I'd say it's fine!

[DmitryArefiev]

@cbjeukendrup Cool. Thanks!