We can easily avoid the burden of checking if the lexer was
initialized prior to calling destroy by the caller, let's do it.

This allows simplification in state tracking with the following patch,
"qmp: add QmpSession" can call qmp_session_destroy() multiple times,
which in turns calls json_lexer_destroy().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 qobject/json-lexer.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/qobject/json-lexer.c b/qobject/json-lexer.c
index 632320d72d..fa7a2c43a8 100644
--- a/qobject/json-lexer.c
+++ b/qobject/json-lexer.c
@@ -361,5 +361,8 @@ void json_lexer_flush(JSONLexer *lexer)
 
 void json_lexer_destroy(JSONLexer *lexer)
 {
-    g_string_free(lexer->token, true);
+    if (lexer->token) {
+        g_string_free(lexer->token, true);
+        lexer->token = NULL;
+    }
 }
-- 
2.21.0.196.g041f5ea1cf