Fixed canvas size limitations issue & fixed removal of all colors from palette

[itsamrit]

Now whenever user types invalid input in width and height box. It says to please enter valid input

[unsettledgames]

Hi there! Thanks for the contribution, first of all could you please edit the PR so that it merges into lospec:master instead of lospec:bug-fixes?

[itsamrit]

Okay, I'll do it.