imap_perform_authentication: fix memory leak

Coverity CID 1215296. There's a potential risk for a memory leak in
here, and moving the free call to be unconditional seems like a cheap
price to remove the risk.

lib/imap.c

@@ -634,8 +634,6 @@ static CURLcode imap_perform_authentication(struct connectdata *conn)
     if(mech && (imapc->preftype & IMAP_TYPE_SASL)) {
       /* Perform SASL based authentication */
       result = imap_perform_authenticate(conn, mech, initresp, state1, state2);
-
-      Curl_safefree(initresp);
     }
     else if((!imapc->login_disabled) &&
             (imapc->preftype & IMAP_TYPE_CLEARTEXT))
@@ -648,6 +646,8 @@ static CURLcode imap_perform_authentication(struct connectdata *conn)
     }
   }
 
+  Curl_safefree(initresp);
+
   return result;
 }