Fix build

Author: nyalldawson

src/core/geometry/qgslinestringv2.cpp

@@ -308,7 +308,7 @@ void QgsLineStringV2::append( const QgsLineStringV2* line )
   else
   {
     // if append line does not have z coordinates, fill with 0 to match number of points in final line
-    mZ.insert( mZ.count(), mX.size() - mZ.size(), 0 );
+    mZ.insert( mZ.count(), mCoords.size() - mZ.size(), 0 );
   }
 
   if ( line->is3D() )
@@ -318,7 +318,7 @@ void QgsLineStringV2::append( const QgsLineStringV2* line )
   else
   {
     // if append line does not have m values, fill with 0 to match number of points in final line
-    mM.insert( mM.count(), mX.size() - mM.size(), 0 );
+    mM.insert( mM.count(), mCoords.size() - mM.size(), 0 );
   }
 
   mBoundingBox = QgsRectangle(); //set bounding box invalid