Silent warnings from creating exception

Apparently this can lead to strange errors on some setups:

    Accessing static property Exception::$trace as non static

Fixes phpmyadmin/phpmyadmin#12791

Signed-off-by: Michal Čihař <michal@cihar.com>

Author: nijel

src/Context.php

@@ -457,7 +457,7 @@ public static function load($context = '')
             $context = self::$contextPrefix . $context;
         }
         if (!class_exists($context)) {
-            throw new LoaderException(
+            throw @new LoaderException(
                 'Specified context ("' . $context . '") does not exist.',
                 $context
             );