Updates CoreExtension::twig_constant to check for definition first to avoid hard crash

src/Extension/CoreExtension.php

@@ -1329,6 +1329,10 @@ function twig_constant($constant, $object = null)
         $constant = \get_class($object).'::'.$constant;
     }
 
+    if (!\defined($constant)) {
+        throw new RuntimeError(sprintf('Constant "%s" is undefined.', $constant));
+    }
+
     return \constant($constant);
 }