Zero Window Size Bug

[cohaereo]

Both position and size can get reset to zero/very low negative values, causing alkahest to crash on startup.
This usually happens when you close alkahest while it's minimized (you love to see it).

This bug has been plaguing me and users for ages, so it's time I violently bashed it's head in and subsequently cremated it:

• Alkahest should prevent weird window dimensions from being written to the config (eg. while minimized)
• Window dimensions should be verified upon startup, and reset if they're invalid
• Hold a victory ceremony