Truncate long file names in MediaDownloader

Fixes #344

DiscordChatExporter.Domain/Exporting/MediaDownloader.cs

@@ -46,7 +46,7 @@ namespace DiscordChatExporter.Domain.Exporting
             var originalFileName = Regex.Match(url, @".+/([^?]*)").Groups[1].Value;
 
             var fileName = !string.IsNullOrWhiteSpace(originalFileName)
-                ? originalFileName
+                ? $"{Path.GetFileNameWithoutExtension(originalFileName).Truncate(50)}{Path.GetExtension(originalFileName)}"
                 : GetRandomFileName();
 
             return PathEx.EscapePath(fileName);

DiscordChatExporter.Domain/Internal/Extensions/StringExtensions.cs

@@ -4,6 +4,11 @@ namespace DiscordChatExporter.Domain.Internal.Extensions
 {
     internal static class StringExtensions
     {
+        public static string Truncate(this string str, int charCount) =>
+            str.Length > charCount
+                ? str.Substring(0, charCount)
+                : str;
+
         public static StringBuilder AppendIfNotEmpty(this StringBuilder builder, char value) =>
             builder.Length > 0
                 ? builder.Append(value)