Fix: make get_noble_color return exactly 1 QColor

get_noble_color was crashing accessing an empty list
when m_nobles.values() returned an empty list.

If m_nobles.values() returns 1 color return that, otherwise
if it returns no colors or many colors return a default value.
Merge pull request #177 from stoutheart/crash-get_noble_color

Fix: make get_noble_color return exactly 1 QColor