fixed null pointer. This nullpointer could happen if the first buffer
did not contain more than 58 bytes (header).

14:11:41.960 [NETTY-TOMP2P - worker-client/server - -1-1] ERROR
n.tomp2p.message.TomP2PCumulationTCP - Error in TCP decoding
java.lang.NullPointerException: null
at
net.tomp2p.message.TomP2PCumulationTCP.decoding(TomP2PCumulationTCP.java:76)
~[tomp2p-core-5.0-Alpha.094d47d-SNAPSHOT.jar:na]