Fixed curve preview color issue by assigning a preview canvas on the …

[aadame3311]

Before: when using background color while drawing a curve, the color would revert back to foreground until the curve was finished drawing. This pull request fixes the issue by assigning a preview canvas to the curve tool, which eventually draws unto the canvas when the 'draw_curve' gets called on the Curve tool.

[aadame3311]

Please review new commit. You brought up a good point about the draw_curve function.

[1j01]

I think all that's left here is to clean up the commit history. It should just be one commit, with no noisy whitespace changes. I can do this if you want, but do you want to have a go at it? I can help with git if you get stuck.

[aadame3311]

Cleaned up commit history

[1j01]

I manually merged this in https://github.com/1j01/jspaint/commit/5f64f1c251c4d34be827f797e17d3f1dafc89890

• Removed whitespace changes and irrelevant package lock file changes
• Updated to work with a tweak to the drawing strategy
• Updated to use a changed variable name (main_canvas)

Thanks!