Hello!

I discovered that there's a memory leak in the pgtk code, if the windows are
created/destroyed/moved/shrunk/widened frequently. I've verified it with
profiler that this indeed is the location (https://i.imgur.com/LnrgGyj.png) and
fixed it (https://i.imgur.com/zdgnn5K.png).

PS: This is my first time sending a patch, I'm not 100% sure if this is
how it's done.

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Kind Regards,
Sharaf Zaman