Fix for disappearing Oekaki tabs

[Nick]

I've now fixed a problem where if you had an Oekaki tab open in the background for a long time on Chromium-based browsers (Google Chrome, Edge, Brave) when you returned to the tab it would refresh itself and lose your drawing progress. It's still a good idea to save often, though!

[beko]

huzzah!

[Sapphirescript]

Aww! I remember struggling all the time when I used to use web based programs for this reason. I'm so glad minor distractions don't mean the end for the hours!

[Saphhirefox]

thank you nick i will give you my firstborn son if i ever have kids i rarely draw but when i do this was annoying thanku thankyou thankhdhasdhw