libcman: fix possible string nontermination: node name
Haven't tested it, but it seems that if node.cn_name has 254 non-null
bytes (should be otherwise perfectly valid, actual characters number
may vary due to utf-8), it will pester later in the processing due
to not being null-terminated (depends whether 255th byte being
accidentally zero), strcmp in find_node_by_name being the first
troublesome place in row.
After this change and taking preceding condition into account,
the situation should be safe.