Fix possible memory leak and an uninitialized variable issue

I checked my project (which is using NMSSH via cocoapods) with the static analyzer from Xcode 5.1 and found several issues, which I fixed in this pull request:
* Apple recommends against accessing C pointers via properties, if you pass them to CoreFoundation C functions. (Could leak memory in some cases)I removed the readwrite property and used the instance variable directly in your CF calls. The readonly property from the header file can remain.
* The variable erc might be used uninitialized ("garbage value"), I set it to 0
* I moved one `int rc = 0;` declaration because the result was not used until some lines below

Now, the Xcode Analyzer is happy again :)

Best regards,
Clemens