Simplify Curved Types for QgsPostgresFeatureIterator

Currently curved types are never simplified PostgreSQL server side.

However in many datasets just a small fraction of the dataset features
has curves.

The existing code already has a "st_simplifypreservetopology"
branch which will simplify Linestrings and Polygons and leaves
other geometries unchanged. Use this code for curved geometry layers.

src/providers/postgres/qgspostgresfeatureiterator.cpp

@@ -514,8 +514,7 @@ bool QgsPostgresFeatureIterator::declareCursor( const QString &whereClause, long
 
     if ( !mRequest.simplifyMethod().forceLocalOptimization() &&
          mRequest.simplifyMethod().methodType() != QgsSimplifyMethod::NoSimplification &&
-         QgsWkbTypes::flatType( QgsWkbTypes::singleType( usedGeomType ) ) != QgsWkbTypes::Point &&
-         !QgsWkbTypes::isCurvedType( usedGeomType ) )
+         QgsWkbTypes::flatType( QgsWkbTypes::singleType( usedGeomType ) ) != QgsWkbTypes::Point )
     {
       // PostGIS simplification method to use
       QString simplifyPostgisMethod;
@@ -524,7 +523,7 @@ bool QgsPostgresFeatureIterator::declareCursor( const QString &whereClause, long
       bool postSimplification;
       postSimplification = false; // default to false. Set to true only for PostGIS >= 2.2 when using st_removerepeatedpoints
 
-      if ( mRequest.simplifyMethod().methodType() == QgsSimplifyMethod::OptimizeForRendering )
+      if ( !QgsWkbTypes::isCurvedType( usedGeomType ) && mRequest.simplifyMethod().methodType() == QgsSimplifyMethod::OptimizeForRendering )
       {
         // Optimize simplification for rendering
         if ( mConn->majorVersion() < 2 )