GWHAT crashes and fails to open afterwards if it failed to fetch the climate station database the first time it is started.

[jnsebgosselin]

GWHAT tries to fetch the climate station database from the EC ftp server the first time it is opened.

If this operation fails, no error is issued and an empty file is saved, which causes GWHAT to crash afterwards when trying to load the climate station list. Following attempts to open GWHAT also result in a crash.

The operation of fetching the climate station database should be made more robust and it should not systematically crash the program when it fails. Moreover, this operation should not be done on startup, but only when the Weather Stations Browser is opened for the first time.