Make --list-* exit code be 0

Previously it returned the sum of listed things because ???. This
was completely useless and in many ways actively counterproductive
because of the success/failure conventions around exit codes.

Closes #1410

include/internal/catch_session.cpp

@@ -288,8 +288,9 @@ namespace Catch {
                 applyFilenamesAsTags( *m_config );
 
             // Handle list request
-            if( Option<std::size_t> listed = list( m_config ) )
-                return static_cast<int>( *listed );
+            if (list(m_config)) {
+                return 0;
+            }
 
             TestGroup tests { m_config };
             auto const totals = tests.execute();