WRG: m_NbPixel to unsigned long (comparaison between signed and unsigned)

Modules/Filtering/Contrast/include/otbComputeGainLutFilter.h

@@ -114,7 +114,7 @@ private:
   double m_Max;
   double m_Step;
   unsigned int m_NbBin;
-  long m_NbPixel;
+  unsigned long m_NbPixel;
 
 };