Fixed class normalization for class map case.

src/Composer/Autoload/ClassLoader.php

@@ -162,14 +162,14 @@ class ClassLoader
      */
     public function findFile($class)
     {
-        if (isset($this->classMap[$class])) {
-            return $this->classMap[$class];
-        }
-
         if ('\\' == $class[0]) {
             $class = substr($class, 1);
         }
 
+        if (isset($this->classMap[$class])) {
+            return $this->classMap[$class];
+        }
+
         if (false !== $pos = strrpos($class, '\\')) {
             // namespaced class name
             $classPath = str_replace('\\', DIRECTORY_SEPARATOR, substr($class, 0, $pos)) . DIRECTORY_SEPARATOR;