Bug if first sentence scores 0

[kirefu]

Hi there,

This error is produced:
totalMatchingCount[order] += bestMatchingCount[order]
UnboundLocalError: local variable 'bestMatchingCount' referenced before assignment

chrF/chrF++.py

Line 157 in 6d3c384

bestMatchingCount = matchingNgramCounts

when the first sentence scores 0. Therefore I believe the fix is that all these variables inside the if statement should be initialised to defaultdict(float) in case of this.