Support missing .po files (#2068)

* [V3 Core] Support missing .po files

* Modified if-state

* Use PEP8 recommendation for empty list check

https://www.python.org/dev/peps/pep-0008/#programming-recommendations

redbot/core/core_commands.py

@@ -1066,6 +1066,9 @@ class Core(CoreLogic):
             red_dist = pkg_resources.get_distribution("red-discordbot")
             red_path = Path(red_dist.location) / "redbot"
             locale_list = sorted(set([loc.stem for loc in list(red_path.glob("**/*.po"))]))
+            if not locale_list:
+                await ctx.send("No languages found.")
+                return
             pages = pagify("\n".join(locale_list))
 
         await ctx.send_interactive(pages, box_lang="Available Locales:")