Merge version matching for rar and unrar. This is ever so slightly slower in theory for unrar 5.x because there's an additional unnecessary `sscanf()` call, but it's not actually gonna matter, and saves quite a bit of duplicated logic. This also makes the matching a bit more safe by verifying `sscanf()` actually worked, and avoids using a uninitialized `version` value due to an unexpected input. Finally, this makes the parsing a bit more strict by requiring a version number after the `RAR` and `UNRAR` line prefixes -- leading not to using the uninitialized version variable. This will be required by the upcoming unrar-free support as it reports a `RAR archive ...` line that would have matched the `RAR` version check.