fix: previous session.close read&write error

Signed-off-by: Kingtous <kingtous@qq.com>

src/flutter.rs

@@ -179,7 +179,6 @@ impl Session {
     /// Close the session.
     pub fn close(&self) {
         self.send(Data::Close);
-        let _ = SESSIONS.write().unwrap().remove(&self.id);
     }
 
     /// Reconnect to the current session.

src/flutter_ffi.rs

@@ -133,6 +133,7 @@ pub fn session_close(id: String) {
     if let Some(session) = SESSIONS.read().unwrap().get(&id) {
         session.close();
     }
+    let _ = SESSIONS.write().unwrap().remove(&id);
 }
 
 pub fn session_refresh(id: String) {