Fix -Wcatch-value in sexpr.cpp

This is fixed by catching bty const-ref, rather than by value.

Also a few trailing space deletions.

utils/kicad2step/sexpr/sexpr.cpp

@@ -469,7 +469,7 @@ namespace SEXPR
 					throw std::invalid_argument( "unsupported argument type, this shouldn't have happened" );
 				}
 			}
-			catch( INVALID_TYPE_EXCEPTION )
+			catch( const INVALID_TYPE_EXCEPTION& )
 			{
 				return i;
 			}