GUI: File browser should start from selected path

[antoniou79]

My suggestion is that it would be more friendly if, when clicking the (browse/set) button next to a path field that has been set to a custom folder, eg. the fields on the Global Options->Paths tab, then the browser should start the user from that selected custom folder, provided that it is still a valid and accessible folder.

The following observations are from testing on Windows 10 x64 with ScummVM 2.7.0git (built from master HEAD). I don't know as of yet if behavior is different on other ports, but it is likely.

Currently, at least on Windows:

• if *not* using the system's native browser, ScummVM starts the user from the "browser_lastpath" which is where the user last navigated to using the browser. If that path no longer exists, or the config "browser_lastpath" key is not set, then ScummVM will start the user from the "current" directory (where ScummVM is executed from (?)).
• if using the system's native file browser (Windows' Exporer), it keeps track of the last folder the user chose independently from the config "browser_lastpath" key. If that last folder no longer exists, it falls back to the current directory, same as above. I think I've seen it once fall back to the Documents folder, but I may be misremembering.

Note: Selection to use or not use the system's file browser is done from Global Options -> Misc -> Use native system file browser (checkbox)