fix: correct mapping of edge label properties in plots when loops are present

[schochastics]

Fix #157

library(igraph)
g <- make_graph(c(1, 2, 1, 1, 2, 3), directed = F)
cols <- c('red','green','blue')
plot(g, edge.color = cols, edge.label.color = cols, edge.label = cols)

Also fixed font, family and cex

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