Fix of [prusa3d/PrusaSlicer] Remove unnecessary null pointer checks (#5813)

Don't use
if (ptr)
	delete ptr;
call
delete ptr;
directly, it contains the test for null ptr.

src/slic3r/GUI/ExtraRenderers.cpp

@@ -49,7 +49,6 @@ BitmapTextRenderer::~BitmapTextRenderer()
 {
 #ifdef SUPPORTS_MARKUP
     #ifdef wxHAS_GENERIC_DATAVIEWCTRL
-    if (m_markupText)
     delete m_markupText;
     #endif //wxHAS_GENERIC_DATAVIEWCTRL
 #endif // SUPPORTS_MARKUP

src/slic3r/GUI/GUI_Preview.cpp

@@ -36,10 +36,7 @@ View3D::View3D(wxWindow* parent, Model* model, DynamicPrintConfig* config, Backg
 
 View3D::~View3D()
 {
-    if (m_canvas != nullptr)
     delete m_canvas;
-
-    if (m_canvas_widget != nullptr)
     delete m_canvas_widget;
 }
 

src/slic3r/GUI/Plater.cpp

@@ -595,16 +595,9 @@ struct Sidebar::priv
 
 Sidebar::priv::~priv()
 {
-    if (object_manipulation != nullptr)
     delete object_manipulation;
-
-    if (object_settings != nullptr)
     delete object_settings;
-
-    if (frequently_changed_parameters != nullptr)
     delete frequently_changed_parameters;
-
-    if (object_layers != nullptr)
     delete object_layers;
 }