Make sure we always generate one keypool key at minimum

src/wallet/wallet.cpp

@@ -2950,9 +2950,9 @@ bool CWallet::TopUpKeyPool(unsigned int kpSize)
         // generate +20% internal keys (minimum 2 keys)
         int64_t amountExternal = KeypoolCountExternalKeys();
         int64_t amountInternal = setKeyPool.size() - amountExternal;
-        int64_t targetInternal = max((int64_t)ceil(nTargetSize * 0.2), (int64_t) 2);
-        int64_t missingExternal = max( (int64_t)(nTargetSize - amountExternal), (int64_t) 0);
-        int64_t missingInternal = max(targetInternal - amountInternal, (int64_t) 0);
+        int64_t targetInternal = std::max((int64_t)ceil(nTargetSize * 0.2), (int64_t) 2);
+        int64_t missingExternal = std::max(std::max((int64_t) nTargetSize, (int64_t) 1) - amountExternal, (int64_t) 0);
+        int64_t missingInternal = std::max(targetInternal - amountInternal, (int64_t) 0);
 
         if (!IsHDEnabled() || !CanSupportFeature(FEATURE_HD_SPLIT))
         {