Array tool: when changing axis numbering, default to valid numbering

Otherwise, when you change the axis numbering type, and don't update
the start offset string, you get an error on dialog save. Instead,
if the number isn't valid, change it to a valid one.

pcbnew/dialogs/dialog_create_array.cpp

@@ -262,6 +262,44 @@ void DIALOG_CREATE_ARRAY::OnSelectCenterButton( wxCommandEvent& event )
 }
 
 
+void DIALOG_CREATE_ARRAY::OnAxisNumberingChange( wxCommandEvent& aEvent )
+{
+    // On an alphabet change, make sure the offset control is valid by default.
+
+    const unsigned newAlphabet = aEvent.GetSelection();
+
+    wxCHECK( newAlphabet >= 0 && newAlphabet < numberingTypeData.size(), /* void */ );
+
+    const ARRAY_AXIS::NUMBERING_TYPE numberingType =
+            numberingTypeData[newAlphabet].m_numbering_type;
+
+    wxTextCtrl* matchingTextCtrl = nullptr;
+
+    if( aEvent.GetEventObject() == m_choicePriAxisNumbering )
+        matchingTextCtrl = m_entryGridPriNumberingOffset;
+    else if( aEvent.GetEventObject() == m_choiceSecAxisNumbering )
+        matchingTextCtrl = m_entryGridSecNumberingOffset;
+    else if( aEvent.GetEventObject() == m_choiceCircNumbering )
+        matchingTextCtrl = m_entryCircNumberingStart;
+
+    wxCHECK( matchingTextCtrl, /* void */ );
+
+    ARRAY_AXIS dummyAxis;
+    dummyAxis.SetAxisType( numberingType );
+
+    // If the text control has a valid value for the new alphabet, keep it
+    // else reset to the first value in the new alphabet.
+
+    const bool isAlreadyOK = dummyAxis.SetOffset( matchingTextCtrl->GetValue() );
+
+    if( !isAlreadyOK )
+    {
+        dummyAxis.SetOffset( ARRAY_AXIS::TypeIsNumeric( numberingType ) ? 1 : 0 );
+        matchingTextCtrl->SetValue( dummyAxis.GetItemNumber( 0 ) );
+    }
+}
+
+
 // Implement the RECEIVER interface for the callback from the TOOL
 void DIALOG_CREATE_ARRAY::UpdatePickedItem( const EDA_ITEM* aItem )
 {