facebook-api: Fix id assertion in fb_api_cb_publish_mst()

[oliverralbertini]

Sometimes id comes back as 1, but whether it's 1 or 2, fb_thrift_read_str() seems to do the right thing. This prevents crashes of this nature:

facebook - Error: Failed to read thrift: facebook-api.c:1548 fb_api_cb_publish_mst: assertion 'id == 2'

Note this happens when connected to a workplace account, in case others haven't seen it.

[dequis]

Thank you!