Fix adapt crash for mixed-element 2D meshes with frozen quad layers

[como2099]

This PR fixes a crash in PUMI adapt that occurs for 2D mixed-element meshes (tri + quad) when quad layers are frozen.

The issue was discovered while using PUMI with CFD workflow. In this configuration, adaptation should proceed on triangle elements even when quad layers are excluded.

The fix adds a guard in maQuality.cc to allow safe adaptation of triangles in mixed-element 2D meshes without affecting existing workflows.

Bug originally found in release v4.1.0; tested by building against current develop and running the affected adaptation path.

Fixes #523