launcher: Await user input on error

[wjt]

Previously, if the Godot editor failed to launch (perhaps because it has not been downloaded!), the terminal window would disappear too quickly for the error message to be legible.

Add the same "Press Enter to continue..." prompt as in the updater, but only in
the error case. Handle two error paths:

• The process could not be spawned
• The process was spawned but exited with a non-zero status

[wjt]

The case where we hit this was that I manually prepared a moddable-pong-with-patchwork bundle from @jgbourque as follows:

1. git clone https://github.com/endlessm/moddable-pong.git
2. Copy update-patchwork.exe and launch-patchwork.exe into the project & update .gitignore
3. Zip up the folder
4. Send it to Justin

I meant to tell Justin to run update-patchwork.exe (to actually install the addon & editor) before launch-patchwork.exe. But I did not. So when he tried to use launch-patchwork.exe it just flashed a terminal on the screen for a split second.

[wjt]

I must confess to only having tested this on Linux!