Fix a segfault if we try to close a nullpointer.

Same local or in the smb plugin.

modules/csync_smb.c

@@ -104,6 +104,10 @@ static int _close(csync_vio_method_handle_t *fhandle) {
   int rc = -1;
   smb_fhandle_t *handle = NULL;
 
+  if (fhandle == NULL) {
+    return -1;
+  }
+
   handle = (smb_fhandle_t *) fhandle;
 
   rc = smbc_close(handle->fd);

src/vio/csync_vio_local.c

@@ -72,6 +72,10 @@ int csync_vio_local_close(csync_vio_method_handle_t *fhandle) {
   int rc = -1;
   fhandle_t *handle = NULL;
 
+  if (fhandle == NULL) {
+    return -1;
+  }
+
   handle = (fhandle_t *) fhandle;
 
   rc = close(handle->fd);