verify: allow empty/no trigger file

If we use a trigger timeout, we don't need the file.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/init.c b/init.c
index c7fdcdd..108f2b8 100644
--- a/init.c
+++ b/init.c
@@ -2212,8 +2212,10 @@
 			}
 
 			sz = split - optarg;
-			trigger_file = calloc(1, sz + 1);
-			strncpy(trigger_file, optarg, sz);
+			if (sz) {
+				trigger_file = calloc(1, sz + 1);
+				strncpy(trigger_file, optarg, sz);
+			}
 
 			split++;
 			cmd = trigger_cmd = strdup(split);