[BOLT] fix the endless loop of --iterative-guess

Solve the endless loop caused by iterative guess. The main function of this option is guessEdgeByIterativeApproach, where the do while loop involves guessPredEdgeCounts and guessSuccessEdgeCounts. In some scenarios, the do while loop will fall into an endless loop. The reason is that although the GuessedPredEdgeCounts function has guessed the pred-edges counts, GuessedArcs does not insert the corresponding BB block, resulting in the changed variable always being true.

Reviewed By: rafauler
Differential Revision: https://reviews.llvm.org/D154922