Server not giving WMS compliant error messages for invalid time/elevation data

[Joern Ungermann]

The WMS server has an internal exception that is not caught and thus gives a wrong indication to the client. Likely a bug introduced by refactoring.

[Reimar Bauer]

Catch exception thrown, when no file is available for chosen timestep.

Resolve issue #205

→ <<cset d10f143f9300>>