Fix prepare for PooledStatement

src/AbstractPool.php

@@ -72,7 +72,7 @@ abstract class AbstractPool implements Pool
 
         $this->connections = $connections = new \SplObjectStorage;
         $this->idle = $idle = new \SplQueue;
-        $this->prepare = coroutine($this->callableFromInstanceMethod("doPrepare"));
+        $this->prepare = coroutine($this->callableFromInstanceMethod("createStatement"));
 
         $idleTimeout = &$this->idleTimeout;
 
@@ -338,6 +338,13 @@ abstract class AbstractPool implements Pool
     public function prepare(string $sql): Promise
     {
         return call(function () use ($sql) {
+            $statement = yield from $this->createStatement($sql);
+            return new PooledStatement($this, $statement, $this->prepare);
+        });
+    }
+
+    private function createStatement(string $sql): \Generator
+    {
         $connection = yield from $this->pop();
         \assert($connection instanceof Link);
 
@@ -358,8 +365,7 @@ abstract class AbstractPool implements Pool
             $this->push($connection);
         });
 
-            return new PooledStatement($this, $statement, $this->prepare);
+        return $statement;
-        });
     }
 
     /**