Ignore initially specified labels for buttons with wxBU_NOTEXT

It doesn't make much sense to specify a non-empty label and wxBU_NOTEXT style
together, but if this happens, the label should be ignored, as it was already
done by wxGTK, but not wxMSW and wxOSX -- so add the missing checks for
wxBU_NOTEXT to these ports too.

Closes #17152.

src/msw/button.cpp

@@ -82,7 +82,10 @@ bool wxButton::Create(wxWindow *parent,
                       const wxValidator& validator,
                       const wxString& name)
 {
-    wxString label(lbl);
+    wxString label;
+    if ( !(style & wxBU_NOTEXT) )
+    {
+        label = lbl;
         if (label.empty() && wxIsStockID(id))
         {
             // On Windows, some buttons aren't supposed to have mnemonics
@@ -94,6 +97,7 @@ bool wxButton::Create(wxWindow *parent,
                             : wxSTOCK_WITH_MNEMONIC
                     );
         }
+    }
 
     if ( !CreateControl(parent, id, pos, size, style, validator, name) )
         return false;

src/osx/button_osx.cpp

@@ -69,6 +69,8 @@ bool wxButton::Create(wxWindow *parent,
 
     wxString label;
 
+    if ( !(style & wxBU_NOTEXT) )
+    {
         // Ignore the standard label for help buttons if possible, they use "?"
         // label under Mac which looks better.
         if ( !IsHelpButtonWithStandardLabel(id, labelOrig) )
@@ -76,6 +78,7 @@ bool wxButton::Create(wxWindow *parent,
             label = labelOrig.empty() && wxIsStockID(id) ? wxGetStockLabel(id)
                                                          : labelOrig;
         }
+    }
 
 
     if ( !wxButtonBase::Create(parent, id, pos, size, style, validator, name) )