tag: Do not unref a NULL write message

After successfully writing a tag, the next read might fail in which case
tag_read_cb may be called several times. The pending write_msg pointer
needs to be unrefed only once.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/tag.c b/src/tag.c
index fbc71c3..1d07f8b 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -284,8 +284,10 @@ static void tag_read_cb(uint32_t adapter_idx, uint32_t target_idx, int status)
 	if (!tag)
 		return;
 
-	dbus_message_unref(tag->write_msg);
-	tag->write_msg = NULL;
+	if (tag->write_msg) {
+		dbus_message_unref(tag->write_msg);
+		tag->write_msg = NULL;
+	}
 
 	__near_adapter_start_check_presence(adapter_idx, target_idx);