toString method called by the debugger should not change the state of the BtcBlock object

[SergioDemianLerner]

The method toString is called by the debugger many times during a debug session, even if the debug window is not open.
The BtcBlock.java class implements the following code:

    public String toString() {
        StringBuilder s = new StringBuilder();
        s.append(" block: \n");
        s.append("   hash: ").append(getHashAsString()).append('\n');

But the method getHashAsString modifies the internal state:

    public String getHashAsString() {
        return getHash().toString();
    }
  @Override
    public Sha256Hash getHash() {
        if (hash == null)
            hash = calculateHash();
        return hash;
    }

Therefore the method getHashAsString / getHash methods should be replaced by:

    public String toString() {
        StringBuilder s = new StringBuilder();
        s.append(" block: \n");
        s.append("   hash: ").append(getHashAsStringDebug()).append('\n');

.....
    public String getHashAsStringDebug() {
        return getHash().toString();
    }
....
    public Sha256Hash getHashDebug() {
        Sha256Hash  localHash = calculateHash();
        return localHash;
    }