Add custom height check back

This was dropped while dealing with merge conflict in "implement index parallel sync".

Author: Sjors

src/index/base.cpp

@@ -264,6 +264,13 @@ void BaseIndex::Sync()
         return;
     }
 
+    // If pindex_next is our first block and we are starting from a custom height,
+    // set pindex to be the previous block. This ensures we test that we can still rewind
+    // from our custom start height in the event of a reorg.
+    if (pindex_next->nHeight == m_start_height && m_start_height > 0) {
+        pindex = pindex_next->pprev;
+    }
+
     // Handle potential reorgs; if the next block's parent doesn't match our current tip,
     // rewind our index state to match the chain and resume from there.
     if (pindex_next->pprev != pindex && !Rewind(pindex, pindex_next->pprev)) {
@@ -415,6 +422,13 @@ void BaseIndex::Sync()
                 break;
             }
 
+            // If pindex_next is our first block and we are starting from a custom height,
+            // set pindex to be the previous block. This ensures we test that we can still rewind
+            // from our custom start height in the event of a reorg.
+            if (pindex_next->nHeight == m_start_height && m_start_height > 0) {
+                pindex = pindex_next->pprev;
+            }
+
             // New blocks arrived during sync.
             // Handle potential reorgs; if the next block's parent doesn't match our tip,
             // rewind index state to the correct chain, then resume.