Fix Alembic point cloud streaming.

Point clouds are not imported and read anymore. This was caused by an
API change in rB128eb6cbe928e58dfee1c64f340fd8d663134c26 which was not
applied to `AbcPointsReader`. It did not cause a compile error as the
base class as a default implementation for this method.

source/blender/io/alembic/intern/abc_reader_points.h

@@ -44,6 +44,8 @@ class AbcPointsReader : public AbcObjectReader {
   struct Mesh *read_mesh(struct Mesh *existing_mesh,
                          const Alembic::Abc::ISampleSelector &sample_sel,
                          int read_flag,
+                         const char *velocity_name,
+                         const float velocity_scale,
                          const char **err_str);
 };