[py3] Fix comparison of cardinality when maxc is graph_nodes.INFINITY
`max(maxc, maxvalue)` would evaluate to `max("Infinity", <some integer>)` when maxc is graph_nodes.INFINITY. While this works on python2 (by chance, since strings and integers can be compared), this does not on python3. We thus move the "if" that checks for graph_nodes.INFINITY inside the "for" loop.
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