improve map quality when map width != height
improve map quality when map width != height

Whenever the width and height of a map differ, choose the smaller one for calculating the visible tile level.
As a result, the tile level is increased earlier, leading to higher-resolution results.

Tested with the schangen1689 map theme.

CCMAIL: 2d26968b5807d2ab2a0d758156a2fbf6c613f711@joanneum.at

Earthwings/marble,adraghici/marble,tzapzoor/marble,tzapzoor/marble,David-Gil/marble-dev,rku/marble,tzapzoor/marble,David-Gil/marble-dev,oberluz/marble,tzapzoor/marble,David-Gil/marble-dev,adraghici/marble,adraghici/marble,utkuaydin/marble,quannt24/marble,utkuaydin/marble,probonopd/marble,rku/marble,tucnak/marble,quannt24/marble,oberluz/marble,Earthwings/marble,oberluz/marble,utkuaydin/marble,David-Gil/marble-dev,tucnak/marble,David-Gil/marble-dev,quannt24/marble,rku/marble,Earthwings/marble,adraghici/marble,tucnak/marble,utkuaydin/marble,Earthwings/marble,tzapzoor/marble,oberluz/marble,Earthwings/marble,adraghici/marble,AndreiDuma/marble,probonopd/marble,rku/marble,AndreiDuma/marble,AndreiDuma/marble,probonopd/marble,probonopd/marble,quannt24/marble,utkuaydin/marble,probonopd/marble,oberluz/marble,tucnak/marble,quannt24/marble,tucnak/marble,David-Gil/marble-dev,rku/marble,tzapzoor/marble,Earthwings/marble,probonopd/marble,AndreiDuma/marble,quannt24/marble,AndreiDuma/marble,tzapzoor/marble,rku/marble,utkuaydin/marble,quannt24/marble,tzapzoor/marble,oberluz/marble,probonopd/marble,tucnak/marble,AndreiDuma/marble,adraghici/marble,tucnak/marble