fabrics: do no try do disconnect invalid ctrl

The ctrl object (child) can be NULL when either discovery is false or
_nvmf_discovery fails. Thus only disconnect when it is a valid pointer.

Signed-off-by: Daniel Wagner <[email protected]>

Author: igaw

libnvme/src/nvme/fabrics.c

@@ -2256,7 +2256,7 @@ static int _nvmf_discovery(struct nvme_global_ctx *ctx,
 			if (discover)
 				_nvmf_discovery(ctx, fctx, true, child);
 
-			if (disconnect) {
+			if (child && disconnect) {
 				nvme_disconnect_ctrl(child);
 				nvme_free_ctrl(child);
 			}