Correct insert of KeyValNode into []Node
Correct insert of KeyValNode into []Node

The append logic in structureKeyValueNode was incorrect and could result
in a slice out of range error (#42). Correctly insert KeyValNode into nn
and update nn length.

fixes #42

TelnetMike/go-fuzz,zhuyue1314/go-fuzz,gregory-m/go-fuzz,stephens2424/go-fuzz,btracey/go-fuzz,ebfe/go-fuzz,bmbernie/go-fuzz,gregory-m/go-fuzz,pmezard/go-fuzz,TelnetMike/go-fuzz,pmezard/go-fuzz,ebfe/go-fuzz,bmbernie/go-fuzz,btracey/go-fuzz,zhuyue1314/go-fuzz,pierrec/go-fuzz,dgryski/go-fuzz,h8liu/go-fuzz,pierrec/go-fuzz,stephens2424/go-fuzz,dgryski/go-fuzz,h8liu/go-fuzz