Fix leak when a transform error occurs while transforming linestrings

(cherry-picked from 4af5ff5)

Author: nyalldawson

src/core/geometry/qgslinestring.cpp

@@ -786,24 +786,23 @@ int QgsLineString::dimension() const
 
 void QgsLineString::transform( const QgsCoordinateTransform &ct, QgsCoordinateTransform::TransformDirection d, bool transformZ )
 {
-  double *zArray = mZ.data();
-
+  double *zArray = nullptr;
   bool hasZ = is3D();
   int nPoints = numPoints();
-  bool useDummyZ = !hasZ || !transformZ;
-  if ( useDummyZ )
+
+  // it's possible that transformCoords will throw an exception - so we need to use
+  // a smart pointer for the dummy z values in order to ensure that they always get cleaned up
+  std::unique_ptr< double[] > dummyZ;
+  if ( !hasZ || !transformZ )
   {
-    zArray = new double[nPoints];
-    for ( int i = 0; i < nPoints; ++i )
-    {
-      zArray[i] = 0;
-    }
+    dummyZ.reset( new double[nPoints]() );
+    zArray = dummyZ.get();
   }
-  ct.transformCoords( nPoints, mX.data(), mY.data(), zArray, d );
-  if ( useDummyZ )
+  else
   {
-    delete[] zArray;
+    zArray = mZ.data();
   }
+  ct.transformCoords( nPoints, mX.data(), mY.data(), zArray, d );
   clearCache();
 }