Check that number of points passed to wxDC::DrawSpline() is at least 2

DoDrawSpline() implementations for all ports work for the number of points
>= 2 (for 2 points there is drawn a straight line) so we need to add checks
whether this requirement is met.

See #19172.

interface/wx/dc.h

@@ -714,7 +714,7 @@ public:
     /**
         Draws a spline between all given points using the current pen.
 
-        The number of points must be at least 3 for the spline to be drawn.
+        The number of points must be at least 2 for the spline to be drawn.
 
         @beginWxPerlOnly
         Not supported by wxPerl.

src/common/dcbase.cpp

@@ -903,16 +903,14 @@ static void wx_spline_draw_point_array(wxDC *dc)
 void wxDCImpl::DoDrawSpline( const wxPointList *points )
 {
     wxCHECK_RET( IsOk(), wxT("invalid window dc") );
+    wxCHECK_RET(points, "NULL pointer to spline points?");
+    wxCHECK_RET(points->GetCount() >= 2, "incomplete list of spline points?");
 
     const wxPoint *p;
     double cx1, cy1, cx2, cy2;
     double           x1, y1, x2, y2;
 
     wxPointList::compatibility_iterator node = points->GetFirst();
-    if (!node)
-        // empty list
-        return;
-
     p = node->GetData();
 
     x1 = p->x;

src/common/dcgraph.cpp

@@ -846,6 +846,8 @@ void wxGCDCImpl::DoDrawLines(int n, const wxPoint points[],
 void wxGCDCImpl::DoDrawSpline(const wxPointList *points)
 {
     wxCHECK_RET( IsOk(), wxT("wxGCDC(cg)::DoDrawSpline - invalid DC") );
+    wxCHECK_RET(points, "NULL pointer to spline points?");
+    wxCHECK_RET(points->GetCount() >= 2, "incomplete list of spline points?");
 
     if ( !m_logicalFunctionSupported )
         return;
@@ -853,10 +855,6 @@ void wxGCDCImpl::DoDrawSpline(const wxPointList *points)
     wxGraphicsPath path = m_graphicContext->CreatePath();
 
     wxPointList::compatibility_iterator node = points->GetFirst();
-    if ( !node )
-        // empty list
-        return;
-
     const wxPoint *p = node->GetData();
 
     wxCoord x1 = p->x;

src/generic/dcpsg.cpp

@@ -1463,6 +1463,8 @@ void wxPostScriptDCImpl::SetLogicalFunction(wxRasterOperationMode WXUNUSED(funct
 void wxPostScriptDCImpl::DoDrawSpline( const wxPointList *points )
 {
     wxCHECK_RET( m_ok, wxT("invalid postscript dc") );
+    wxCHECK_RET(points, "NULL pointer to spline points?");
+    wxCHECK_RET(points->GetCount() >= 2, "incomplete list of spline points?");
 
     SetPen( m_pen );
 

src/gtk/print.cpp

@@ -1716,6 +1716,9 @@ void wxGtkPrinterDCImpl::DoDrawEllipse(wxCoord x, wxCoord y, wxCoord width, wxCo
 #if wxUSE_SPLINES
 void wxGtkPrinterDCImpl::DoDrawSpline(const wxPointList *points)
 {
+    wxCHECK_RET(points, "NULL pointer to spline points?");
+    wxCHECK_RET(points->GetCount() >= 2, "incomplete list of spline points?");
+
     SetPen (m_pen);
 
     double c, d, x1, y1, x3, y3;

src/msw/dc.cpp

@@ -1158,10 +1158,10 @@ void wxMSWDCImpl::DoDrawSpline(const wxPointList *points)
     // B2 = (2*P1 + P2)/3
     // B3 = P2
 
-    wxASSERT_MSG( points, wxT("NULL pointer to spline points?") );
+    wxCHECK_RET( points, "NULL pointer to spline points?" );
 
     const size_t n_points = points->GetCount();
-    wxASSERT_MSG( n_points > 2 , wxT("incomplete list of spline points?") );
+    wxCHECK_RET( n_points >= 2 , "incomplete list of spline points?" );
 
     const size_t n_bezier_points = n_points * 3 + 1;
     POINT *lppt = new POINT[n_bezier_points];