dot11decrypt: Fix a resource leak on error path

Coverity CID 1450217

Change-Id: I51a3c3cca5c3850a2f8e9de5b4cca9f0efaca4a8
Reviewed-on: https://code.wireshark.org/review/36705
Reviewed-by: Anders Broman <a.broman58@gmail.com>

epan/crypt/dot11decrypt.c

@@ -385,6 +385,7 @@ Dot11DecryptRc4KeyData(const guint8 *decryption_key, guint decryption_key_len,
     }
     decrypted_key = (guint8 *)g_memdup(encrypted_keydata, encrypted_keydata_len);
     if (!decrypted_key) {
+        gcry_cipher_close(rc4_handle);
         return NULL;
     }