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 in the qmp-async RFC
series, the patch "qmp: add QmpSession" can call qmp_session_destroy()
multiple time, 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 e1745a3d95..39969047f4 100644
--- a/qobject/json-lexer.c
+++ b/qobject/json-lexer.c
@@ -351,5 +351,8 @@ 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;
+    }
 }
-- 
2.18.0.547.g1d89318c48