Viewport id (DXF code 69) is always equal to 0

[mlightcad]

Step to reproduce the issue:

1. Read the attached dwg file "layout.dwg".
2. Read viewport entities in "*Paper_Space" block table record
3. Read their property "id" (DXF code 69)

Results:

There are two viewport entities in "*Paper_Space" block table record. Viewport id of two entities is 0.

Expected

Viewport id of one entity is 1. Another is 2.

layout.zip