[MachineOutliner] Fix uninitialized variable warnings. NFCI.

struct Candidate {

private:

  /// The start index of this \p Candidate in the instruction list.

  unsigned StartIdx;

  unsigned StartIdx = 0;

  /// The number of instructions in this \p Candidate.

  unsigned Len;

  unsigned Len = 0;

  // The first instruction in this \p Candidate.

  MachineBasicBlock::iterator FirstInst;

  MachineBasicBlock::iterator LastInst;

  // The basic block that contains this Candidate.

  MachineBasicBlock *MBB;

  MachineBasicBlock *MBB = nullptr;

  /// Cost of calling an outlined function from this point as defined by the

  /// target.

  unsigned CallOverhead;

  unsigned CallOverhead = 0;

public:

  /// The index of this \p Candidate's \p OutlinedFunction in the list of

  /// \p OutlinedFunctions.

  unsigned FunctionIdx;

  unsigned FunctionIdx = 0;

  /// Identifier denoting the instructions to emit to call an outlined function

  /// from this point. Defined by the target.

  unsigned CallConstructionID;

  unsigned CallConstructionID = 0;

  /// Contains physical register liveness information for the MBB containing

  /// this \p Candidate.

  /// Ukkonen's algorithm.

  struct ActiveState {

    /// The next node to insert at.

    SuffixTreeNode *Node;

    SuffixTreeNode *Node = nullptr;

    /// The index of the first character in the substring currently being added.

    unsigned Idx = EmptyIdx;