Merge bitcoin#10775: nCheckDepth chain height fix

d9d1bd3 nCheckDepth chain height fix (romanornr)

Pull request description:

  ````
  if (nCheckDepth <= 0)
      nCheckDepth = 1000000000; // suffices until the year 19000
  if (nCheckDepth > chainActive.Height())
      nCheckDepth = chainActive.Height();
  ````

  These lines confuse me.
  Correct me if I am wrong, but we can't check any more blocks than we have right?
  If someone requests <= 0 it get set it into some huge number and then immediately limit it to the chain height in the following statement.
  ````
  if (nCheckDepth > chainActive.Height())
      nCheckDepth = chainActive.Height();
  ````
  when using ````--checkblocks=Z```` When Z is ````0```` or any other negative number, it will check all blocks.

  I think it should be changed to this maybe.
  ````
  if (nCheckDepth <= 0 || nCheckDepth > chainActive.Height())
      nCheckDepth = chainActive.Height();
  ````
  Which gets rid of that huge number which is confusing for any other altcoins that have a different block time.

Tree-SHA512: 8ee0ae5f33b399fa74dc16926709694ccfe1fc8a043cba2f5d00884220ac1b9b13f2df4588041f4133be634e5c7b14f4eebe24294028dafe91581a97dbe627f3

src/validation.cpp

@@ -3841,9 +3841,7 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     auto dbTx = evoDb->BeginTransaction();
 
     // Verify blocks in the best chain
-    if (nCheckDepth <= 0)
-        nCheckDepth = 1000000000; // suffices until the year 19000
-    if (nCheckDepth > chainActive.Height())
+    if (nCheckDepth <= 0 || nCheckDepth > chainActive.Height())
         nCheckDepth = chainActive.Height();
     nCheckLevel = std::max(0, std::min(4, nCheckLevel));
     LogPrintf("Verifying last %i blocks at level %i\n", nCheckDepth, nCheckLevel);