FastTree crashes if input topology tree has polytomies

[tnguyencfe]

When an input topology tree for the "-intree" option of FastTree has polytomies, FastTree will crash with error:
FastTree: FastTree.c:4267: SetProfile: Assertion `c->nChild == 2' failed

Used command line: FastTree -gtr -nt -gamma -nosupport -nome -mllen -intree ...

Affects TestTopology.py unit tests