C#: Address review comments

Author: hvitved

csharp/extractor/Semmle.Extraction.CSharp/Analyser.cs

@@ -456,7 +456,7 @@ public bool LogRoslynArgs(string[] roslynArgs, string extractorVersion)
             bool argsWritten;
             using (var streamWriter = new StreamWriter(new FileStream(tempFile, FileMode.Append, FileAccess.Write)))
             {
-                streamWriter.WriteLine($"# Arguments to Roslyn: {string.Join(' ', roslynArgs)}");
+                streamWriter.WriteLine($"# Arguments to Roslyn: {string.Join(' ', roslynArgs.Where(arg => !arg.StartsWith('@')))}");
                 argsWritten = roslynArgs.WriteCommandLine(streamWriter);
             }
 

csharp/extractor/Semmle.Util/CommandLineExtensions.cs

@@ -15,15 +15,16 @@ public static class CommandLineExtensions
         /// <returns>True iff the file was written.</returns>
         public static bool WriteCommandLine(this IEnumerable<string> commandLineArguments, TextWriter textWriter)
         {
-            foreach (var arg in commandLineArguments.Where(arg => arg[0] == '@').Select(arg => arg.Substring(1)))
+            var found = false;
+            foreach (var arg in commandLineArguments.Where(arg => arg.StartsWith('@')).Select(arg => arg.Substring(1)))
             {
                 string line;
                 using (StreamReader file = new StreamReader(arg))
                     while ((line = file.ReadLine()) != null)
                         textWriter.WriteLine(line);
-                return true;
+                found = true;
             }
-            return false;
+            return found;
         }
     }
 }