Fixed [4.0 b2.1] Corrupted (in memory) tabs when closing other tab

[Wanderer]

Let's say there are 2 different databases (i.e. mame 0.162 and mame 0.163 or another non-mame db). Load both databases in two separate tabs and then close one of them. Clicking on any tree branch in the remaining window (database or rom path) shows... nothing! It's as if the other database has also been closed/unloaded. This also happens with three dbs. As soon as one of them is closed, it seems as if all the others are also unloaded from memory, even though the tabs remain open. The DB tree branches and the defined rom paths are shown but when clicking on them, no contents are shown.