[ClassLoader] Got an if-condition out of a unnecessary loop

src/Composer/Autoload/ClassLoader.php

@@ -181,8 +181,8 @@ class ClassLoader
         $classPath .= str_replace('_', DIRECTORY_SEPARATOR, $className) . '.php';
 
         foreach ($this->prefixes as $prefix => $dirs) {
-            foreach ($dirs as $dir) {
+			if (0 === strpos($class, $prefix)) {
-                if (0 === strpos($class, $prefix)) {
+				foreach ($dirs as $dir) {
                     if (file_exists($dir . DIRECTORY_SEPARATOR . $classPath)) {
                         return $dir . DIRECTORY_SEPARATOR . $classPath;
                     }