Canvas size no limitations

[flabbet]

Describe the bug
So right now, create new pixel doesn't have any restrains. I can put anything there, and in result editor breaks, there is no canvas.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://apps.lospec.com/pixel-editor/
2. Enter -123 to width and 9999 to height
3. Click Create

Expected behavior
Input should forbit user to enter invalid values.

Screenshots

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Brave
• Version: 1.35.103 Chromium: 98.0.4758.102 (Official Build) (64-bit)](https://brave.com/latest/)

[unsettledgames]

Note to myself: write a few input validation functions so that we can reuse them

[itsamrit]

Can you please assign this issue to me?

[unsettledgames]

Done, thanks for offering :)