fix: move mock_mining check to get_utxos() caller while preserving behaviour (returning error), #5841

Author: fdefelici

testnet/stacks-node/src/burnchains/bitcoin_regtest_controller.rs

@@ -744,11 +744,6 @@ impl BitcoinRegtestController {
         utxos_to_exclude: Option<UTXOSet>,
         block_height: u64,
     ) -> Option<UTXOSet> {
-        // if mock mining, do not even bother requesting UTXOs
-        if self.config.get_node_config(false).mock_mining {
-            return None;
-        }
-
         let pubk = if self.config.miner.segwit && epoch_id >= StacksEpochId::Epoch21 {
             let mut p = *public_key;
             p.set_compressed(true);
@@ -1693,6 +1688,11 @@ impl BitcoinRegtestController {
             // in RBF, you have to consume the same UTXOs
             utxos
         } else {
+            // if mock mining, do not even bother requesting UTXOs
+            if self.config.node.mock_mining {
+                return Err(BurnchainControllerError::NoUTXOs);
+            }
+
             // Fetch some UTXOs
             let addr = self.get_miner_address(epoch_id, public_key);
             match self.get_utxos(