Fix pool queue dequeuing loop

This resolves a problem introduced with the pool.reconfigure() enhancement.

Author: Christopher Jones

lib/pool.js

@@ -27,14 +27,17 @@ const util = require('util');
 // _checkRequestQueue()
 //   When a connection is returned to the pool, this method is called (via an
 // event handler) to determine when requests for connections should be
-// completed and cancels any timeout that may have been associated with the
+// resumed and cancels any timeout that may have been associated with the
 // request. This method is also called from reconfigure() so that waiting
-// connection-requests can be processed.
+// connection requests can be processed. Note the use of a local variable for
+// the number of connections out. This is because the connection requests will
+// not resume until after the loop is finished, and therefore the number of
+// connections the pool thinks is out will not be incremented.
 //-----------------------------------------------------------------------------
 function _checkRequestQueue() {
-  while (this._connRequestQueue.length > 0 &&
-      this._connectionsOut < this.poolMax) {
-    // process the payload
+  let connectionsOut = this._connectionsOut;
+  while (this._connRequestQueue.length > 0 && connectionsOut < this.poolMax) {
+    connectionsOut += 1;
     const payload = this._connRequestQueue.shift();
     if (this._enableStatistics) {
       this._totalRequestsDequeued += 1;