[DowngradePhp80] Add DowngradeSubstrFalsyRector

Author: samsonasik

rules/DowngradePhp80/Rector/FuncCall/DowngradeSubstrFalsyRector.php

@@ -51,8 +51,11 @@ public function refactor(Node $node): ?Node
             return null;
         }
 
-        if ($node instanceof Ternary && ! $node->if instanceof Expr) {
-            $node->cond->setAttribute(self::IS_UNCASTABLE, true);
+        if ($node instanceof Ternary) {
+            if ($node->if instanceof Expr) {
+                $node->cond->setAttribute(self::IS_UNCASTABLE, true);
+            }
+
             return null;
         }