Don't crash raster shader with nan or inf values (fix #15444)

(cherry-picked from 34ebe12)

src/core/raster/qgscolorrampshader.cpp

@@ -88,6 +88,9 @@ bool QgsColorRampShader::shade( double theValue, int* theReturnRedValue, int* th
   {
     return false;
   }
+  if ( qIsNaN( theValue ) || qIsInf( theValue ) )
+    return false;
+
   int colorRampItemListCount = mColorRampItemList.count();
   int idx;
   if ( !mLUTInitialized )

tests/src/python/CMakeLists.txt

@@ -69,6 +69,7 @@ ADD_PYTHON_TEST(PyQgsPoint test_qgspoint.py)
 ADD_PYTHON_TEST(PyQgsRangeWidgets test_qgsrangewidgets.py)
 ADD_PYTHON_TEST(PyQgsRasterFileWriter test_qgsrasterfilewriter.py)
 ADD_PYTHON_TEST(PyQgsRasterLayer test_qgsrasterlayer.py)
+ADD_PYTHON_TEST(PyQgsRasterColorRampShader test_qgsrastercolorrampshader.py)
 ADD_PYTHON_TEST(PyQgsRectangle test_qgsrectangle.py)
 ADD_PYTHON_TEST(PyQgsRelation test_qgsrelation.py)
 ADD_PYTHON_TEST(PyQgsRelationManager test_qgsrelationmanager.py)

tests/src/python/test_qgsrastercolorrampshader.py

@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsColorRampShader.
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+
+__author__ = 'Nyall Dawson'
+__date__ = '17/08/2016'
+__copyright__ = 'Copyright 2016, The QGIS Project'
+# This will get replaced with a git SHA1 when you do a git archive
+__revision__ = '$Format:%H$'
+
+import qgis  # NOQA
+
+
+from qgis.PyQt.QtGui import QColor
+
+from qgis.core import (QgsColorRampShader)
+from qgis.testing import unittest
+
+
+class TestQgsRasterColorRampShader(unittest.TestCase):
+
+    def testNan(self):
+        shader = QgsColorRampShader()
+
+        item1 = QgsColorRampShader.ColorRampItem(1, QColor(0, 0, 0))
+        item2 = QgsColorRampShader.ColorRampItem(2, QColor(255, 255, 255))
+        shader.setColorRampItemList([item1, item2])
+        self.assertFalse(shader.shade(float('NaN'))[0])
+        self.assertFalse(shader.shade(float("inf"))[0])
+
+if __name__ == '__main__':
+    unittest.main()