Check the output state for recorded workspaces

Sway records pid, workspace, and output for every new process. However, if the
output gets disabled and the workspace disappears, the workspace is still
re-created on the disabled output. This commit adds a check for the enabled
flag, so that NULL will be passed to workspace_create() in this case.

sway/tree/root.c

@@ -270,7 +270,16 @@ found:
 			sway_log(SWAY_DEBUG,
 					"Creating workspace %s for pid %d because it disappeared",
 					pw->workspace, pid);
-			ws = workspace_create(pw->output, pw->workspace);
+
+			struct sway_output *output = pw->output;
+			if (pw->output && !pw->output->enabled) {
+				sway_log(SWAY_DEBUG,
+						"Workspace output %s is disabled, trying another one",
+						pw->output->wlr_output->name);
+				output = NULL;
+			}
+
+			ws = workspace_create(output, pw->workspace);
 		}
 
 		pid_workspace_destroy(pw);