Prevent reload on modules that failed to initialize

See comment in sopel-irc#1399

sopel/modules/reload.py

@@ -46,7 +46,10 @@ def f_reload(bot, trigger):
         bot.setup()
         return bot.reply('done')
 
-    if name not in sys.modules and name not in sopel.loader.enumerate_modules(
+    # Use OR instead of AND because modules that fail to load will not have been
+    # added to sys.modules; `reload_module_tree` should not even be reached if
+    # reload is attempted on a module that failed to load in the first place.
+    if name not in sys.modules or name not in sopel.loader.enumerate_modules(
             bot.config):
         return bot.reply('"%s" not loaded, try the `load` command' % name)