Fix LaunchAndFocus and ship AppLauncher keys in the default retrobat.ini

[goldorakiller]

This PR groups two related follow-ups on the launcher. It started as the LaunchAndFocus fix alone and now also carries the AppLauncher ini fix.

1. LaunchAndFocus (review feedback from @Tartifless)

• The black splash could stay on screen indefinitely. SplashVideo.CloseBlackSplash() was only called on the success path (esHandle != IntPtr.Zero && !isExternalLauncher). When the window handle was never obtained — exclusive fullscreen, or EmulationStation exiting early — it was never closed there. It is now closed unconditionally right after the wait loop, which is bounded by maxWaitMs and therefore always reached, with a finally as a safety net in case an exception is thrown earlier.

• Missing return false in the catch. return true sat after the try/catch, so a failure to start EmulationStation was logged and then reported as a success. return true moved to the end of the try, return false added to the catch, and the XML doc updated to match the new contract.

2. AppLauncher missing from a generated retrobat.ini

The option was documented but never showed up in a freshly generated retrobat.ini. It was written as AppLauncher= with an empty value, and IniFile.ToString() skips entries whose value is empty, so the line was dropped as soon as the file was saved. Users had to add the key by hand to discover the feature.

• The default ini now ships AppLauncher="" and AppLauncher2="" as real keys. "" is not an empty string, so the lines survive every rewrite, and an empty value still means "disabled" as documented.
• The number of supported entries is now a single constant (MaxAppLaunchers) shared with the ini comment, instead of a magic 20 duplicated in both places.
• An entry with no path is skipped silently, since that is the state every default install ships with. An entry whose path is set but does not exist is still logged as a warning.

Reading the configuration never writes to retrobat.ini: entries are read with GetValue, so absent keys stay absent. A key manually emptied down to AppLauncher= is therefore still dropped on the next save, which is pre-existing IniFile behaviour and simply leaves the feature disabled.

Generated [RetroBat] section

; Path to an additional application to launch in parallel with RetroBat (.exe, .bat, .cmd...). Leave empty to disable. Use quotes if the path contains spaces.
; Add -nowindow at the end to start it without a visible window (e.g. AppLauncher="C:\tools\app.exe" -nowindow). Without -nowindow, it starts normally.
; Up to 20 applications can be launched: fill in AppLauncher below, then add AppLauncher2, AppLauncher3... up to AppLauncher20.
AppLauncher=""
AppLauncher2=""

Testing

Release build passes with no warnings. The ini behaviour was checked with a standalone harness driving IniFile + RetroBatConfigLoader over three scenarios: fresh generation, a full rewrite triggered by a missing key, and a real path set by the user. The AppLauncher lines and their values survive in all three, and loading the configuration leaves the file untouched.Follow-up to review feedback on #48.

• The black splash was only closed inside the success branch (esHandle != IntPtr.Zero && !isExternalLauncher). When the main window handle was never obtained - exclusive fullscreen, or EmulationStation exiting early - it stayed on screen for the whole wait. It is now closed unconditionally right after the (bounded) wait loop, with a finally block as a safety net if an exception is thrown earlier. CloseBlackSplash is idempotent, so the extra call is harmless.

• The method returned true even when an exception was caught, so callers could not distinguish a successful launch from a failed one. The success return is now at the end of the try block and the catch returns false. The XML doc was updated to match the new contract.