Mesh: Clear loose edges bitmap with count of zero

When there are no loose edges, the loose edge bitmap shouldn't be used.
That was already documented in the loose edge storage struct, but the
bit vector wasn't actually cleared.

source/blender/blenkernel/intern/mesh_runtime.cc

@@ -124,7 +124,9 @@ const blender::bke::LooseEdgeCache &Mesh::loose_edges() const
         count--;
       }
     }
-
+    if (count == 0) {
+      loose_edges.clear_and_shrink();
+    }
     r_data.count = count;
   });
 
@@ -135,7 +137,7 @@ void Mesh::loose_edges_tag_none() const
 {
   using namespace blender::bke;
   this->runtime->loose_edges_cache.ensure([&](LooseEdgeCache &r_data) {
-    r_data.is_loose_bits.resize(0);
+    r_data.is_loose_bits.clear_and_shrink();
     r_data.count = 0;
   });
 }