[ErrorHandler] fix throwing from __toString()

src/Symfony/Component/Debug/ErrorHandler.php

@@ -401,7 +401,7 @@ class ErrorHandler
         $scope = $this->scopedErrors & $type;
 
         if (4 < $numArgs = \func_num_args()) {
-            $context = $scope ? (func_get_arg(4) ?: []) : [];
+            $context = func_get_arg(4) ?: [];
             $backtrace = 5 < $numArgs ? func_get_arg(5) : null; // defined on HHVM
         } else {
             $context = [];