Add bounds checking when slicing SHAPE_LINE_CHAIN from the middle of the last arc.

(and said arc is the last shape in the chain)

Fixes https://gitlab.com/kicad/code/kicad/-/issues/18391

libs/kimath/src/geometry/shape_line_chain.cpp

@@ -1481,7 +1481,7 @@ const SHAPE_LINE_CHAIN SHAPE_LINE_CHAIN::Slice( int aStartIndex, int aEndIndex )
         const SHAPE_ARC& arcToSplit = Arc( arcToSplitIndex );
 
         // Copy the points as arc points
-        for( size_t i = aStartIndex; arcToSplitIndex == ArcIndex( i ); i++ )
+        for( size_t i = aStartIndex; i < m_points.size() && arcToSplitIndex == ArcIndex( i ); i++ )
         {
             rv.m_points.push_back( m_points[i] );
             rv.m_shapes.push_back( { rv.m_arcs.size(), SHAPE_IS_PT } );