Remove unnecessary null pointer checks

[elfring]

Extra null pointer checks are not needed in functions like the following.

• CloseCNFAAlsa
• CloseCNFAPulse

[cnlohr]

After a long discussion, because these are very rarely set, the if is there as an indicator to future programmers that these values will very commonly be null. No change willbe made. Thank you for pointing it out, though.

[elfring]

I would prefer source code with less questionable checks.