Segfault when .desktop file does not contain Exec line

If Synapse encounters a .desktop file that does not contain an Exec line then it will segfault and crash as soon as it is launched.

While the Exec line is apparently required, it seems that not all files have the line (e.g. the attached Stellarium manual page from openSUSE). Instead of failing horribly, it would seem safer (and easier for users to understand) if Synapse ignored malformed files.

As a work-around, you can rename the file (if it isn't important to you) or add a dummy "Exec" line.

An alternative cause of the same behaviour could be a malformed file or an incorrectly named file (although I don't know what other checks are done).

This may also be related to bug #1067916, as the errors in the stack trace are the same.