Handle RAR files split with a file splitter

[ci-macpaw]

Originally reported on Google Code with ID 238

allanlibunao:

Before version 2.3, theunarchiver was successfully unpacking files that first needed
to be 
combined and then unrar'd, such as:

  sample.rar.001
  sample.rar.002

With version 2.3, I now get this message:

  Could not extract the file "<insert file name here>": Error on decrunching

Expected results: Opening sample.rar.001 with theunarchiver successfully concats the
files and 
then unrars the result (just like it used to).

I've attached a couple of sample files (~200kb) to help repro my issue.

---

* *Attachment: [sample.rar.001](https://storage.googleapis.com/google-code-attachments/theunarchiver/issue-238/comment-0/sample.rar.001)* * *Attachment: [sample.rar.002](https://storage.googleapis.com/google-code-attachments/theunarchiver/issue-238/comment-0/sample.rar.002)*

[ci-macpaw]

allanlibunao:

Yup, I've been using a separate app to concatenate them first, then use theunarchiver
to do the final unpack.

Thank you for listening, I really appreciate it.

[ci-macpaw]

paracelsus:

Because of the way RAR allows split RAR files to be named almost anything, this is 
pretty much impossible to fix. "sample.rar.001" can mean either that the file is split

by a file splitter, or that it is split by RAR itself, and the way to unpack it in
either 
case is different.

Basically, you should not split rar files with anything but rar itself. That might
not be 
very useful if you got the files from somebody else, though. To work around it, join

the files with another program first.

Maybe I can figure out some magic to fix this, but don't hold your breath.