Fix: Collada import assert with faceless prims

Importing `COLLADAFW::MeshPrimitive::LINES` would assert trying to get
the `material_indices` (these are on the Face Domain -- which does not
exist here).

To resolve, early out if we know we handle LINES.

Probably didnt happen before 45cff837bc

Stumbled over this looking into !120737

Pull Request: https://projects.blender.org/blender/blender/pulls/120738

source/blender/io/collada/MeshImporter.cpp

@@ -646,6 +646,10 @@ void MeshImporter::read_polys(COLLADAFW::Mesh *collada_mesh,
 
     int collada_meshtype = mp->getPrimitiveType();
 
+    if (collada_meshtype == COLLADAFW::MeshPrimitive::LINES) {
+      continue; /* read the lines later after all the rest is done */
+    }
+
     /* Since we cannot set `poly->mat_nr` here, we store a portion of `mesh->mpoly` in Primitive.
      */
     Primitive prim = {face_index, &material_indices.span[face_index], 0};
@@ -797,10 +801,6 @@ void MeshImporter::read_polys(COLLADAFW::Mesh *collada_mesh,
       }
     }
 
-    else if (collada_meshtype == COLLADAFW::MeshPrimitive::LINES) {
-      continue; /* read the lines later after all the rest is done */
-    }
-
     if (mp_has_faces) {
       mat_prim_map[mp->getMaterialId()].push_back(prim);
     }