Don't generate max preview twice
Don't generate max preview twice

If you request a preview of X by Y. And after calculating X and Y are
equal to maxWidth and maxHeight then there is no reason to create a
preview of that size.

Signed-off-by: Roeland Jago Douma <982d370f7dc34a05b4abe8788f899578d515262d@famdouma.nl>

pixelipo/server,nextcloud/server,pixelipo/server,nextcloud/server,andreas-p/nextcloud-server,endsguy/server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,pixelipo/server,andreas-p/nextcloud-server,Ardinis/server,Ardinis/server,endsguy/server,Ardinis/server,pixelipo/server,andreas-p/nextcloud-server,endsguy/server,Ardinis/server,endsguy/server,andreas-p/nextcloud-server,nextcloud/server,pixelipo/server,Ardinis/server,andreas-p/nextcloud-server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,nextcloud/server,endsguy/server