Add missing checks for controller_block_add()'s return value.

	modified:   dt_azimuth/dt_az_safety.c
	modified:   dt_elevation/dt_el_safety.c

controller/dt_azimuth/dt_az_safety.c

@@ -349,7 +349,8 @@ static struct controller_block * block_dt_az_safety_create(char *name, int argc,
 	if (controller_block_param_list_add(safety, params))
 		goto err_output;
 
-	controller_block_add(safety);
+	if (controller_block_add(safety) != 0)
+		goto err_add;
 
 	safety->private->command = controller_command_create(
 	    safety, name, "Recover");
@@ -358,6 +359,7 @@ static struct controller_block * block_dt_az_safety_create(char *name, int argc,
 
 	return safety;
 
+err_add:
 err_output:
 	free(safety->output);
 err_input:

controller/dt_elevation/dt_el_safety.c

@@ -573,7 +573,8 @@ static struct controller_block * block_dt_el_safety_create(char *name, int argc,
 	if (controller_block_param_list_add(safety, params))
 		goto err_output;
 
-	controller_block_add(safety);
+	if (controller_block_add(safety) != 0)
+		goto err_add;
 
 	safety->private->command = controller_command_create(
 	    safety, name, "Recover");
@@ -582,6 +583,7 @@ static struct controller_block * block_dt_el_safety_create(char *name, int argc,
 
 	return safety;
 
+err_add:
 err_output:
 	free(safety->output);
 err_input: