according new behavior of SubDiv2D

* Correction for computeBinaryMap crash:
- the function staticSaliencyFineGrained::computeSaliency() outputs a
normalized floating point image
- Add an assert in StaticSaliency::computeBinaryMap in order to check
image depth (must be CV_32F)

* - Change assert in cv::Saliency::StaticSaliency::computeBinaryMap()
- Change normalization factor in cv::Saliency::StaticSaliencyFineGrained::computeSaliencyImpl()

no need to append null-terminated symbol