Missing sharedassets0.assets file in language patch does not terminate install

[drojf]

Currently, if a matching sharedassets0.assets file is not found in the language patch, the installer will just hope for the best and use the default one.

It may be a better idea to stop the install with an error if this happens.

I think the way it works currently is that we extract the whole language patch archive directly, which automatically overwrites the sharedassets0.assets. But it may be better to leave the install as-is, without the language patch installed, if we know for sure it won't work.

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Also see #192 if this is still to be treated as a warning, not an error