Support Requests with HTTPBodyStream

There's an issue when Nocilla is trying to work with requests those have HTTPBodyStream  
The main problem is that Nocilla doesn't handling case, when NSInputStream (HTTPBodyStream) returns 0 on read: method.  
https://developer.apple.com/library/ios/documentation/cocoa/reference/foundation/Classes/NSInputStream_Class/Reference/Reference.html#//apple_ref/occ/instm/NSInputStream/read:maxLength:  
Documentation says that if stream returns 0, it means that buffer endeded and there's no more bytes to read  
"0 indicates that the end of the buffer was reached;"

So this pull request contains fix for described case