use qIsNaN instead of isnan (fixes windows build)

Author: jef-n

src/core/symbology-ng/qgsvectorcolorrampv2.cpp

@@ -30,7 +30,7 @@
 
 static QColor _interpolate( QColor c1, QColor c2, double value )
 {
-  if ( isnan( value ) ) value = 1;
+  if ( qIsNaN(value) ) value = 1;
   int r = ( int )( c1.red() + value * ( c2.red() - c1.red() ) );
   int g = ( int )( c1.green() + value * ( c2.green() - c1.green() ) );
   int b = ( int )( c1.blue() + value * ( c2.blue() - c1.blue() ) );
@@ -370,7 +370,7 @@ QColor QgsRandomColorsV2::color( double value ) const
   int maxVal = 255;
 
   //if value is nan, then use last precalculated color
-  int colorIndex = ( !isnan( value ) ? value : 1 ) * ( mTotalColorCount - 1 );
+  int colorIndex = ( !qIsNaN( value ) ? value : 1 ) * ( mTotalColorCount - 1 );
   if ( mTotalColorCount >= 1 && mPrecalculatedColors.length() > colorIndex )
   {
     //use precalculated hue