Backport of the the commit e903ca5 to old kmplot.

From e903ca56ad26311fcaeb650acf96046c726fb809 Mon Sep 17 00:00:00 2001
From: Albert Astals Cid <aacid@kde.org>
Date: Wed, 23 Mar 2016 20:56:55 +0100
Subject: [PATCH] use std::isnan/isinf since we're including cmath

--- kmplot/view.cpp.orig	2014-09-17 13:01:07 UTC
+++ kmplot/view.cpp
@@ -477,7 +477,7 @@ QPointF View::toPixel( const QPointF & r
 	double x = pixel.x();
 	double y = pixel.y();
 	
-	if ( isnan(x) )
+	if ( std::isnan(x) )
 	{
 		xclipflg = true;
 		x = pixelIfNaN.x();
@@ -497,14 +497,14 @@ QPointF View::toPixel( const QPointF & r
 	}
 	else
 	{
-		if ( isinf(x) == -1 )
+		if ( std::isinf(x) == -1 )
 			x = 0;
 			
-		else if ( isinf(x) == 1 )
+		else if ( std::isinf(x) == 1 )
 			x = m_clipRect.right();
 	}
 	
-	if ( isnan(y) )
+	if ( std::isnan(y) )
 	{
 		yclipflg = true;
 		y = pixelIfNaN.y();
@@ -524,10 +524,10 @@ QPointF View::toPixel( const QPointF & r
 	}
 	else
 	{
-		if ( isinf(y) == -1 )
+		if ( std::isinf(y) == -1 )
 			y = 0;
 		
-		else if ( isinf(y) == 1 )
+		else if ( std::isinf(y) == 1 )
 			y = m_clipRect.bottom();
 	}