Watchonly code: cs_main lock not held #4499

Running Qt compiled with -DDEBUG_LOCKORDER, I'm getting:

Assertion failed: lock cs_main not held in main.cpp:624; locks held:
cs_wallet  wallet.cpp:1078

... call stack is:

(lldb) up
frame [#4](/bitcoin-bitcoin/4/): 0x0000000100287590 bitcoin-qt`IsFinalTx(tx=0x000000011cc9a5d0, nBlockHeight=0, nBlockTime=0) + 80 at main.cpp:624
   621
   622  bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
   623  {
-> 624      AssertLockHeld(cs_main);
   625      // Time based nLockTime implemented in 0.1.6
   626      if (tx.nLockTime == 0)
   627          return true;
(lldb) up
frame [#5](/bitcoin-bitcoin/5/): 0x00000001006802af bitcoin-qt`CWalletTx::IsTrusted(this=0x000000011cc9a5d0) const + 63 at wallet.h:778
   775      bool IsTrusted() const
   776      {
   777          // Quick answer in most cases
-> 778          if (!IsFinalTx(*this))
   779              return false;
   780          int nDepth = GetDepthInMainChain();
   781          if (nDepth >= 1)
(lldb) up
frame [#6](/bitcoin-bitcoin/6/): 0x00000001006c6cfd bitcoin-qt`CWallet::GetWatchOnlyBalance(this=0x000000011cc97da0) const + 765 at wallet.cpp:1082
   1079         for (map<uint256, CWalletTx>::const_iterator it = mapWallet.begin(); it != mapWallet.end(); ++it)
   1080         {
   1081             const CWalletTx* pcoin = &(*it).second;
-> 1082             if (pcoin->IsTrusted())
   1083                 nTotal += pcoin->GetAvailableWatchOnlyCredit();
   1084         }
   1085     }