Add failure if media type could not be determined

CHANGELIST.md

@@ -1,3 +1,7 @@
+### WIP (xxxx-xx-xx)
+
+- Add failure if media type could not be determined
+
 ### 3.4.2 (2025-09-30)
 
 - Fix starting index for CLI

MPF.Frontend/DumpEnvironment.cs

@@ -485,6 +485,8 @@ namespace MPF.Frontend
 
             // Determine the media type from the processor
             MediaType? mediaType = _processor.DetermineMediaType(outputDirectory, outputFilename);
+            if (mediaType == null)
+                return ResultEventArgs.Failure("Could not determine the media type from output files...");
 
             // Extract the information from the output files
             resultProgress.Report(ResultEventArgs.Success("Extracting output information from output files..."));