Prevent overlapping tags

src/Discord.Net.Core/Utils/MentionUtils.cs

@@ -256,6 +256,15 @@ namespace Discord
             if (mode != TagHandling.Remove)
             {
                 Emoji emoji = (Emoji)tag.Value;
+
+                //Remove if its name contains any bad chars (prevents a few tag exploits)
+                for (int i = 0; i < emoji.Name.Length; i++)
+                {
+                    char c = emoji.Name[i];
+                    if (!char.IsLetterOrDigit(c) && c != '_' && c != '-')
+                        return "";
+                }
+
                 switch (mode)
                 {
                     case TagHandling.Name:

src/Discord.Net.Rest/Entities/Messages/MessageHelper.cs

@@ -126,6 +126,7 @@ namespace Discord.Rest
                 index = text.IndexOf("@everyone", index);
                 if (index == -1) break;
 
+                if (!TagOverlaps(tags, index))
                     tags.Add(new Tag<object>(TagType.EveryoneMention, index, "@everyone".Length, 0, null));
                 index++;
             }
@@ -136,12 +137,23 @@ namespace Discord.Rest
                 index = text.IndexOf("@here", index);
                 if (index == -1) break;
 
+                if (!TagOverlaps(tags, index))
                     tags.Add(new Tag<object>(TagType.HereMention, index, "@here".Length, 0, null));
                 index++;
             }
 
             return tags.ToImmutable();
         }
+        private static bool TagOverlaps(IReadOnlyList<ITag> tags, int index)
+        {
+            for (int i = 0; i < tags.Count; i++)
+            {
+                var tag = tags[i];
+                if (index >= tag.Index && index < tag.Index + tag.Length)
+                    return true;
+            }
+            return false;
+        }
         public static ImmutableArray<ulong> FilterTagsByKey(TagType type, ImmutableArray<ITag> tags)
         {
             return tags