Check for undefined in vertical flyout layout function

[rachel-fenichel]

Check for duplicates

• I have searched for similar issues before opening a new one.

Description

In layout_ in flyout_vertical.ts we access the block with const block = item.block. The result is nullable, so all later uses of block have to have a non-null assertion

To fix:

• Check whether block is undefined after setting const block = item.block.
• continue if block doesn't exist.
• Remove ! from after the remaining uses of block within the for loop.

Related to #7522

To get set up for this issue:

• Run npm install from the root of the repository.
• Run npm run build from the root of the repository.
• Run npm run start from the root of the repository to launch the test playground.

[ivalkshfoeif]

Hi @rachel-fenichel, I'd like to work on this issue!

[rashmi29]

Hi @rachel-fenichel , I would like to work on this issue. Could you please assign it to me?

[11aparna91]

Hi @rachel-fenichel , I would like to work on this issue.

[rachel-fenichel]

Hi all, and thanks for your interest! This is being worked on in the blockly-elephant breakout room.