Force enumeration of global collections before using them (#106)

This PR closes #105 

This PR fixes exceptions caused by changing a collection's contents
while it is being enumerated. This can often happen with Guild- and
MemberDatas. By using `ToArray()` on these global collections and using
it in the `foreach` loop, we create a new copy of the collection,
preventing any modification to it.

While this does introduce a lot of memory allocations, there is no
fixing that. Usually, the fix to these exceptions would be to convert
the `foreach` to a reverse-`for`. However, because indices cannot be
used on these collections, that is not possible.

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

src/Commands/RemindCommandGroup.cs

@@ -85,7 +85,7 @@ public class RemindCommandGroup : CommandGroup
         }
 
         var builder = new StringBuilder();
-        for (var i = 0; i < data.Reminders.Count; i++)
+        for (var i = data.Reminders.Count - 1; i >= 0; i--)
         {
             var reminder = data.Reminders[i];
             builder.AppendLine(
@@ -168,8 +168,7 @@ public class RemindCommandGroup : CommandGroup
     [RequireContext(ChannelContext.Guild)]
     [UsedImplicitly]
     public async Task<Result> ExecuteDeleteReminderAsync(
-        [Description("Index of reminder to delete")]
-        [MinValue(0)]
+        [Description("Index of reminder to delete")] [MinValue(0)]
         int index)
     {
         if (!_context.TryGetContextIDs(out var guildId, out _, out var userId))