fix image downscaling

[ebbit1q]

Related Ticket(s)

• Fixes profile picture downscaling does not work #4540

Short roundup of the initial problem

the image was cleared instead of downscaled

What will change with this Pull Request?

• just make a new buffer instead of clearing it

the default size of the database is not 0xfffff but rather 0xffff, on rooster ranges this limit is increased to 0xffffff.
these limits correspond with the sql blob and mediumblob field types, if we want servers to accept the image size we currently enforce on pictures by default we have three options:

• create a smaller definition of profile images at 0xffff, meaning profile pictures will be smaller, we should consider more sophisticated downscaling code on the client side in this case
• make a database migration changing the field from blob to medium blob by default, this is what is currently on rooster ranges
• make a configurable limit that the server enforces, this would mean a protocol expansion to communicate the limit to clients

[ebbit1q]

related #750