[Process] In edge cases getcwd() can return false, then proc_open() should get null to use default value (the working dir of the current PHP process)

src/Symfony/Component/Process/Process.php

@@ -53,7 +53,7 @@ class Process
         }
 
         $this->commandline = $commandline;
-        $this->cwd = null === $cwd ? getcwd() : $cwd;
+        $this->cwd = $cwd;
         if (null !== $env) {
             $this->env = array();
             foreach ($env as $key => $value) {
@@ -359,6 +359,13 @@ class Process
      */
     public function getWorkingDirectory()
     {
+        // This is for BC only
+        if (null === $this->cwd) {
+            // getcwd() will return false if any one of the parent directories does not have
+            // the readable or search mode set, even if the current directory does
+            return getcwd() ?: null;
+        }
+
         return $this->cwd;
     }