GUI: Only default icons in grid view

[chkr-private]

Only default icons are shown in the grid view.

How to reproduce:

• have on old ~/.scummvmrc which does not yet have "enginedid=..." set for the games
• update to scummvm 2.7.0
• got to "Global Option", "GUI"
• "Update Icons"
• in game chooser, switch to grid view

Current result:

• only default tiles/icons are shown

Expected result:

• correct icons

Workaround:

• select a game
• use the gear icon to edit the entry
• no changes, just press "OK" to save
• now the correct game icon is displayed

Comment:

• I checked the difference between my original ~/.scummvmrc file and the one after I applied the workaround for a game and it turns out that in my old .scummvmrc none of the games had an "engineid=" set.
• To avoid the need to update each game individually, probably the engineid could be set fully automatically when starting scummvm.