Image block width and height input fields in inspector allow negative values

[ZebulanStanphill]

The issue

The Width and Height input fields in the block inspector settings for the Image block allow negative values, but of course, that makes no sense, and the min HTML attribute can be used to set the minimum values on the inputs.

Related issues and PRs

• Image resizing should be operable with a keyboard #3977
• No way to lock aspect ratio in Image block when using height/width inputs in inspector #7636
• Image block: width and height input fields in inspector do not start at current values #7638

[designsimply]

Tested and confirmed that I am able to set negative values for image dimensions in the image block.

^{Seen at http://alittletestblog.com/wp-admin/post.php?post=13859&action=edit running WordPress 4.9.6 and Gutenberg 3.1.1 using Firefox 61.0 on macOS 10.13.5.}

[ZebulanStanphill]

Fixed by #7656.