Fix Map JSON loading errors (tgstation#54563)

Also fixes that one runtime everyone runs into when they first load in

code/datums/map_config.dm

@@ -139,9 +139,11 @@
 
 	allow_custom_shuttles = json["allow_custom_shuttles"] != FALSE
 
-	if (!islist(json["jobs_changes"]))
-		log_world("map_config \"job_changes\" field is missing or invalid!")
-		return
+	if ("jobs_changes" in json)
+		if(!islist(json["jobs_changes"]))
+			log_world("map_config \"job_changes\" field is missing or invalid!")
+			return
+		job_changes = json["job_changes"]
 
 	defaulted = FALSE
 	return TRUE

code/modules/admin/verbs/maprotation.dm

@@ -84,6 +84,7 @@
 		VM.map_file = "[map_file]"
 		VM.config_filename = "data/next_map.json"
 		var/json_value = list(
+			"version" = MAP_CURRENT_VERSION,
 			"map_name" = VM.map_name,
 			"map_path" = VM.map_path,
 			"map_file" = VM.map_file,

code/modules/keybindings/setup.dm

@@ -32,7 +32,7 @@
 		var/command = macro_set[key]
 		winset(src, "default-[REF(key)]", "parent=default;name=[key];command=[command]")
 
-	if(prefs.hotkeys)
+	if(prefs?.hotkeys)
 		winset(src, null, "input.focus=true input.background-color=[COLOR_INPUT_ENABLED]")
 	else
 		winset(src, null, "input.focus=true input.background-color=[COLOR_INPUT_DISABLED]")