Handle malformed proxy tag importing correctly

PluralKit.Core/DataFiles.cs

@@ -162,7 +162,8 @@ namespace PluralKit.Bot
                 }
                 else
                 {
-                    member.ProxyTags = dataMember.ProxyTags ?? new ProxyTag[] { };
+                    // Ignore proxy tags where both prefix and suffix are set to null (would be invalid anyway)
+                    member.ProxyTags = (dataMember.ProxyTags ?? new ProxyTag[] { }).Where(tag => !tag.IsEmpty).ToList();
                 }
 
                 member.KeepProxy = dataMember.KeepProxy;

PluralKit.Core/Models.cs

@@ -51,6 +51,8 @@ namespace PluralKit
 
         [JsonIgnore] public string ProxyString => $"{Prefix ?? ""}text{Suffix ?? ""}";
 
+        public bool IsEmpty => Prefix == null && Suffix == null;
+
         public bool Equals(ProxyTag other) => Prefix == other.Prefix && Suffix == other.Suffix;
 
         public override bool Equals(object obj) => obj is ProxyTag other && Equals(other);