Ensure merged line gets selected if either parent is

We were only checking for the selection of a single line that gets
merged.  This prevents the merged line from being highlighted but not
selected after merging

Fixes https://gitlab.com/kicad/code/kicad/issues/10202

(cherry picked from commit addc5574b4)

eeschema/bus-wire-junction.cpp

@@ -268,7 +268,7 @@ bool SCH_EDIT_FRAME::SchematicCleanUp( SCH_SCREEN* aScreen )
 
                     AddToScreen( mergedLine, aScreen );
 
-                    if( firstLine->IsSelected() )
+                    if( firstLine->IsSelected() || secondLine->IsSelected() )
                         selectionTool->AddItemToSel( mergedLine, true /*quiet mode*/ );
 
                     break;