Memory leak and some bugs

[leochangzliao]

For some images, if its height or width less than 32*4 pixels, this line https://github.com/AlexMa011/edgeBoxes-Cpp-version/blob/288c4a6b92d5b104f3202b387029992bcb6c11fd/src/edgesDetect.cpp#L54 will be negative, and this line will break down. My computer will not respond if I run the code many times, and it seems that all my CPU memory used up.