index: Enable reindex-chainstate with active indexes

This is achieved by letting the index sync thread wait until
reindex-chainstate is finished.

This also disables the pruning check when reindexing the chainstate (which is
incompatible with prune mode) because there would be no chain at this point
in init.

src/node/blockstorage.cpp

@@ -27,6 +27,7 @@
 
 namespace node {
 std::atomic_bool fReindex(false);
+std::atomic_bool g_indexes_ready_to_sync{false};
 
 bool CBlockIndexWorkComparator::operator()(const CBlockIndex* pa, const CBlockIndex* pb) const
 {
@@ -940,5 +941,6 @@ void ThreadImport(ChainstateManager& chainman, std::vector<fs::path> vImportFile
         }
     } // End scope of ImportingNow
     chainman.ActiveChainstate().LoadMempool(mempool_path);
+    g_indexes_ready_to_sync = true;
 }
 } // namespace node

src/node/blockstorage.h

@@ -47,6 +47,7 @@ static const unsigned int MAX_BLOCKFILE_SIZE = 0x8000000; // 128 MiB
 static constexpr size_t BLOCK_SERIALIZATION_HEADER_SIZE = CMessageHeader::MESSAGE_START_SIZE + sizeof(unsigned int);
 
 extern std::atomic_bool fReindex;
+extern std::atomic_bool g_indexes_ready_to_sync;
 
 // Because validation code takes pointers to the map's CBlockIndex objects, if
 // we ever switch to another associative container, we need to either use a