Default to all outputs when no output specified

Before, `--output "*"` had to be specified on the cli before
any appearance options if trying to configure all outputs.
However, the manpage states that all outputs would be used by
default if none were specified.

main.c

@@ -411,7 +411,10 @@ static void parse_command_line(int argc, char **argv,
 		"Background Modes:\n"
 		"  stretch, fit, fill, center, tile, or solid_color\n";
 
-	struct swaybg_output_config *config = NULL;
+	struct swaybg_output_config *config = calloc(sizeof(struct swaybg_output_config), 1);
+	config->output = strdup("*");
+	config->mode = BACKGROUND_MODE_INVALID;
+	wl_list_init(&config->link); // init for safe removal
 
 	int c;
 	while (1) {
@@ -422,29 +425,20 @@ static void parse_command_line(int argc, char **argv,
 		}
 		switch (c) {
 		case 'c':  // color
-			if (!config) {
-				goto no_output;
-			}
 			if (!is_valid_color(optarg)) {
 				swaybg_log(LOG_ERROR, "Invalid color: %s", optarg);
 				continue;
 			}
 			config->color = parse_color(optarg);
 			break;
 		case 'i':  // image
-			if (!config) {
-				goto no_output;
-			}
 			free(config->image);
 			config->image = load_background_image(optarg);
 			if (!config->image) {
 				swaybg_log(LOG_ERROR, "Failed to load image: %s", optarg);
 			}
 			break;
 		case 'm':  // mode
-			if (!config) {
-				goto no_output;
-			}
 			config->mode = parse_background_mode(optarg);
 			if (config->mode == BACKGROUND_MODE_INVALID) {
 				swaybg_log(LOG_ERROR, "Invalid mode: %s", optarg);
@@ -500,10 +494,6 @@ static void parse_command_line(int argc, char **argv,
 				: BACKGROUND_MODE_SOLID_COLOR;
 		}
 	}
-	return;
-no_output:
-	fprintf(stderr, "Cannot operate on NULL output config\n");
-	exit(EXIT_FAILURE);
 }
 
 int main(int argc, char **argv) {