Update ftOpticalFlow.cpp
Update ftOpticalFlow.cpp

Fixed bug in getFlowVectors, where width and height were not implemented
julapy/ofxFlowTools,sheridanis/ofxFlowTools,julapy/ofxFlowTools,Nemquae/ofxFlowTools,moostrik/ofxFlowTools,shenberg/ofxFlowTools,moostrik/ofxFlowTools,sheridanis/ofxFlowTools,AntonioModer/ofxFlowTools,AntonioModer/ofxFlowTools