fix file existence test in CAFeature.py
fix file existence test in CAFeature.py

thekingofkings/urban-flow-analysis,thekingofkings/urban-flow-analysis,thekingofkings/urban-flow-analysis,thekingofkings/urban-flow-analysis,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/chicago-crime,thekingofkings/urban-flow-analysis