yanglint BUGFIX memory leak

In case of input file with unknown format (suffix), the input handler
was not correctly freed.
diff --git a/tools/lint/main_ni.c b/tools/lint/main_ni.c
index 8746ba7..78da7f1 100644
--- a/tools/lint/main_ni.c
+++ b/tools/lint/main_ni.c
@@ -381,6 +381,9 @@
 
                 request_expected = 1;
             }
+        } else {
+            ly_in_free(in, 1);
+            in = NULL;
         }
     }