[PATCH] Map preview image for players who don't have the selected map

[elexis]

In alpha 20 and previous versions, there was a clientside error when the host selected a map that the client didn't have. Furthermore the presented mappreview area was entirely magenta.

[elexis]

r18614 attempted to solve this by checking whether the file exists and otherwise picking the default mappreview image.

However that approach only works for clients that have access to PNG files. The released versions on the other side only come with DDS files.

The sprite = foo.png part still works if there are only DDS files available, but the FileExists call does not translate the PNG to DDS, thus always displays the default map preview image to clients with the released version.

[elexis]

In 18905:

Revert r18614 as it doesn't work with the packaged version, refs #4313, because that comes with DDS files instead of PNGs and FileExists does not translate that like the sprite attribute does.

[elexis]

Patch doesn't compile yet, but I'd like to hear whether the approach is entirely stupid.

[Imarok]

Probably should be sovled, be adding a new gui attribute named sprite_fallback, that gets displayed, when the sprite defined in the property sprite doesn't exist.

[Imarok]

Move tickets to Game Setup as UI & Simulation got some sub components.