Fix reload freeze when not modsetting current mode

This fixes the issue of the display freezing on reload with
wlroots#1545.

On master, all output configs are applied on reload. This may cause an
output to have its config applied up to three times, instead of just
once. The three cases are: output name, output identifier, and wildcard.
Not only is this inefficient, but it can cause swaybg to be spawned and
immediately killed.

However, swaybg requires two roundtrips of wl_display (to obtain needed
globals) before it enters its normal event loop. Modesetting will
roundtrip the wl_display. Without modesetting, waitpid for killing
swaybg could block infinitely due to swaybg being blocked by
wl_display_roundtrip.

This only configured an output once. It either uses the wildcard config
or creates an empty wildcard config and applies that. This also fixes a
bug where an output would not be reset when there is no output config to
apply to it.

include/sway/config.h

@@ -586,6 +586,8 @@ struct output_config *store_output_config(struct output_config *oc);
 
 void apply_output_config_to_outputs(struct output_config *oc);
 
+void reset_outputs(void);
+
 void free_output_config(struct output_config *oc);
 
 int workspace_output_cmp_workspace(const void *a, const void *b);

sway/config.c

@@ -471,9 +471,8 @@ bool load_main_config(const char *file, bool is_active, bool validating) {
 	}
 
 	if (is_active) {
-		for (int i = 0; i < config->output_configs->length; i++) {
-			apply_output_config_to_outputs(config->output_configs->items[i]);
-		}
+		reset_outputs();
+
 		config->reloading = false;
 		if (config->swaynag_config_errors.pid > 0) {
 			swaynag_show(&config->swaynag_config_errors);

sway/config/output.c

@@ -391,6 +391,17 @@ void apply_output_config_to_outputs(struct output_config *oc) {
 	}
 }
 
+void reset_outputs(void) {
+	struct output_config *oc = NULL;
+	int i = list_seq_find(config->output_configs, output_name_cmp, "*");
+	if (i >= 0) {
+		oc = config->output_configs->items[i];
+	} else {
+		oc = store_output_config(new_output_config("*"));
+	}
+	apply_output_config_to_outputs(oc);
+}
+
 void free_output_config(struct output_config *oc) {
 	if (!oc) {
 		return;