[Thumb] A branch is not part of an IT block

ReplaceTailWithBranchTo assumed that if an instruction is predicated, it must be part of an IT block. This is not correct for conditional branches.

No testcase as this was triggered by the reverted patch r272017 - test coverage will occur when that patch is re-reverted and there is no known way to trigger this in the meantime.

llvm-svn: 272258