.desktop parser doesn't safely handle malformed files

[kode54]

There are several issues with this parser's naïve .desktop parser:

• If the file doesn't contain a [Desktop Entry] section header, an empty app struct is returned
• If any fields are missing, even if they're necessary for parsing, they're simply left as NULL pointers

There is at least a crash in compare_app_name in either of those cases, if both the name_localized and name fields of any .desktop file are left uninitialized after the struct is calloc'd. Any others may also result in different crashes elsewhere.

I'm not sure which fields are absolutely mandatory for the menu generator to function, so I'll leave it up to someone familiar with the rest of the code to add the necessary validation.

At the very least, all mandatory headers should be checked for presence after parsing the .desktop file, then the app struct should be cleaned up and a NULL returned if the .desktop turns out to be invalid.

The example in my case, somehow, the Arch User Repository package gqrx-nrsc5-git installs an invalid .desktop file in /usr/share/applications, which contains only the following line and nothing more:

StartupNotify=false

(Incidentally, this was caught by a PKGBUILD not being updated past the point of the upstream .desktop file being renamed, which causes it to append a string to a non-existent file and install that in the package.)

[Consolatis]

We should really get the CI going with the test framework and also add an invalid .desktop file like that above to the tests.