This led to a crash when a cape or skin was not stored on disk.
The function caled skins.save_image and returned that function's lwip image object instead of the expected buffer.
skins.save_image also no longer returns the image object because it's not used anywhere
We only use the 'hard stored' mhf_alex skin when it's part of the 'default' query parameter.
In the rare event that mhf_alex is requested but the skin is not accessible, we would fall back to 'mhf_steve' because it's the default for usernames.
This commit adds the special case to use the stored version of the 'mhf_alex' skin when it's not accessible otherwise
