Make GlasbeyLUT at() and size() consistent

Without this, code such as this:

    size_t i = 10000;
    pcl::RGB color = pcl::GlasbeyLUT::at(i % pcl::GlasbeyLUT::size());

... produces the warning "Parameter type mismatch: Values of type
'size_t' may not fit into the receiver type 'unsigned int'".

common/include/pcl/common/colors.h

@@ -59,7 +59,7 @@ namespace pcl
       /** Get a color from the lookup table with a given id.
         *
         * The id should be less than the size of the LUT (see size()). */
-      static RGB at (unsigned int color_id);
+      static RGB at (size_t color_id);
 
       /** Get the number of colors in the lookup table.
         *

common/src/colors.cpp

@@ -300,10 +300,10 @@ static const unsigned char GLASBEY_LUT[] =
 };
 
 /// Number of colors in Glasbey lookup table
-static const unsigned int GLASBEY_LUT_SIZE = sizeof (GLASBEY_LUT) / (sizeof (GLASBEY_LUT[0]) * 3);
+static const size_t GLASBEY_LUT_SIZE = sizeof (GLASBEY_LUT) / (sizeof (GLASBEY_LUT[0]) * 3);
 
 pcl::RGB
-pcl::GlasbeyLUT::at (unsigned int color_id)
+pcl::GlasbeyLUT::at (size_t color_id)
 {
   assert (color_id < GLASBEY_LUT_SIZE);
   pcl::RGB color;