AGS: Running unknown games fails with path error

[tag2015]

After the merge of ​PR 5829, it is no longer possible to start unknown games that have been added using the fallback detection.

Steps to reproduce:

1. Find a game that is not in the detection tables, such as ​this testgame
2. Add the game using the launcher, choose "add anyway"
3. Try to run the game. It'll fail while attempting to load the resources reporting a garbage gamepath.

It should be noted, that the issue only happens for completely unknown games, variants (i.e. games that are in the detection tables, but with different checksum/size) can be run normally.

[tag2015]

After some quick debugging, it seems that the problem occurs when identifyGame calls fallbackDetect.
The fallbackDetectedGame struct should be initialized after fallbackDetect returns, but instead the filesDescriptions array contains garbage.

[tag2015]

Update: I can reproduce the problem using builbot daily builds for windows, but it works properly with my msys2 build using configure options

--disable-all-engines --enable-optimizations --enable-detection-full --enable-engine=ags,director

[bluegr]

Fixed with this PR:
​https://github.com/scummvm/scummvm/pull/6061