simple-wallet-cli: Add warnings about inaccurate balances to to watch-only wallet

src/wallet/wallet2.cpp

@@ -3611,6 +3611,14 @@ bool wallet2::has_multisig_partial_key_images() const
   return false;
 }
 
+bool wallet2::has_unknown_key_images() const
+{
+  for (const auto &td: m_transfers)
+    if (!td.m_key_image_known)
+      return true;
+  return false;
+}
+
 /*!
  * \brief Rewrites to the wallet file for wallet upgrade (doesn't generate key, assumes it's already there)
  * \param wallet_name Name of wallet file (should exist)

src/wallet/wallet2.h

@@ -653,6 +653,7 @@ namespace tools
     bool watch_only() const { return m_watch_only; }
     bool multisig(bool *ready = NULL, uint32_t *threshold = NULL, uint32_t *total = NULL) const;
     bool has_multisig_partial_key_images() const;
+    bool has_unknown_key_images() const;
     bool get_multisig_seed(std::string& seed, const epee::wipeable_string &passphrase = std::string(), bool raw = true) const;
     bool key_on_device() const { return m_key_on_device; }