Provide an optimised constructor for a null QgsRectangle

This is used a lot, yet the current constructor calls the
normalize() method which does a bunch of operations for no
result.

So instead provide a simple optimised null QgsRectangle
constructor and save a lot of cycles.

Refs #17809

Author: nyalldawson

python/core/geometry/qgsrectangle.sip.in

@@ -26,7 +26,10 @@ Examples are storing a layer extent or the current view extent of a map
 #include "qgsrectangle.h"
 %End
   public:
-    QgsRectangle( double xMin = 0, double yMin = 0, double xMax = 0, double yMax = 0 );
+
+    QgsRectangle(); // optimised constructor for null rectangle - no need to call normalize here
+
+    explicit QgsRectangle( double xMin, double yMin = 0, double xMax = 0, double yMax = 0 );
 %Docstring
 Constructor
 %End

src/core/geometry/qgsrectangle.cpp

@@ -32,6 +32,7 @@
 #include "qgspolygon.h"
 #include "qgslinestring.h"
 
+
 QgsRectangle::QgsRectangle( double xMin, double yMin, double xMax, double yMax )
   : mXmin( xMin )
   , mYmin( yMin )

src/core/geometry/qgsrectangle.h

@@ -39,8 +39,12 @@ class QgsBox3d;
 class CORE_EXPORT QgsRectangle
 {
   public:
+
+    //! Constructor for a null rectangle
+    QgsRectangle() = default; // optimised constructor for null rectangle - no need to call normalize here
+
     //! Constructor
-    QgsRectangle( double xMin = 0, double yMin = 0, double xMax = 0, double yMax = 0 );
+    explicit QgsRectangle( double xMin, double yMin = 0, double xMax = 0, double yMax = 0 );
     //! Construct a rectangle from two points. The rectangle is normalized after construction.
     QgsRectangle( const QgsPointXY &p1, const QgsPointXY &p2 );
     //! Construct a rectangle from a QRectF. The rectangle is normalized after construction.
@@ -332,10 +336,10 @@ class CORE_EXPORT QgsRectangle
 
   private:
 
-    double mXmin;
-    double mYmin;
-    double mXmax;
-    double mYmax;
+    double mXmin = 0.0;
+    double mYmin = 0.0;
+    double mXmax = 0.0;
+    double mYmax = 0.0;
 
 };
 

src/providers/wfs/qgswfsshareddata.cpp

@@ -1251,7 +1251,7 @@ QgsRectangle QgsWFSSingleFeatureRequest::getExtent()
     getFeatureUrl.addQueryItem( QStringLiteral( "MAXFEATURES" ), QString::number( 1 ) );
 
   if ( !sendGET( getFeatureUrl, true ) )
-    return -1;
+    return QgsRectangle();
 
   const QByteArray &buffer = response();