Mitigate nil values and change strjoin library

[vanjo9800]

The msrpc.lua and msrpctypes.lua were giving off errors when running the command:
nmap -Pn -p445 --script smb-brute domain.com -d.

The errors in the msrpctypes.lua script came from the migration from bin.pack and bin.unpack to string.pack and string.unpack. The former accepted nil values for as arguments and we did not do any arithmetic to determine whether the data is enough to extract an object. Now, however, we need to manually check whether the data is enough and can no longer pass nil values as arguments. The fix just initializes uninitialized variables to 1 which is the default for Lua.

The errros in the msrpc.lua script came from the wrong library referencing for the strjoin method used in some internal methods. I managed to find it in the stringaux library, not in the stdnse.

[nnposter]

Your patch for the stale references to stdnse.strjoin in library msrpc has been committed as r37721.

[nnposter]

The issue of arithmetic on a potentially nil pos argument is a bit more widespread throughout the msrpctypes library. A patch committed as r37722.

[nnposter]

The fix for ID Authority possibly being nil seems incorrect. See commit r37724 (ef2825b) for an alternate assessment.

[vanjo9800]

Okay, thanks a lot for the fast response to the changes!
I will keep an eye for more issues.

[nnposter]

Thank your for finding the bugs and submitting patches. They are definitely appreciated.

I will tentatively close this issue; we can always reopen it later.