module: Only resolve to _-prefixed filename if needed

* Fixes `test-cwd-enoent-preload.js`
* Minor performance improvement

Author: alexanderGugel

lib/module.js

@@ -193,13 +193,15 @@ Module._findPath = function(request, paths, isMain) {
     var curPath = paths[i];
     if (curPath && stat(curPath) < 1) continue;
 
-    // If _basePath is a symlink, use the real path rather than the path of the
-    // symlink as cache key.
-    var _basePath = path.resolve(curPath, '_' + request);
     var basePath = path.resolve(curPath, request);
+    var filename = tryFindPath(basePath, exts, isMain, isAbsolute)
 
-    var filename = tryFindPath(basePath, exts, isMain, isAbsolute) ||
-      tryFindPath(_basePath, exts, true, isAbsolute);
+    if (!filename) {
+      // If _basePath is a symlink, use the real path rather than the path of
+      // the symlink as cache key.
+      basePath = path.resolve(curPath, '_' + request);
+      filename = tryFindPath(basePath, exts, true, isAbsolute);
+    }
 
     if (filename) {
       // Warn once if '.' resolved outside the module dir