Detect if file is really locked

Sometimes lock file could remain despite no process is locking it. That's the reason we need to detect if it's really locked.
#84

src/Helpers.cs

@@ -135,5 +135,19 @@ public static double GetDouble(string value)
 
             return result;
         }
+
+        public static bool IsFileLocked(string filePath)
+        {
+            try
+            {
+                using FileStream inputStream = File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.None);
+                inputStream.Close();
+            }
+            catch (Exception)
+            {
+                return true;
+            }
+            return false;
+        }
     }
 }

src/LegendaryDownloadManager.xaml.cs

@@ -216,7 +216,8 @@ public void EnqueueMultipleJobs(List<DownloadManagerData.Download> downloadManag
 
         public static async Task WaitUntilLegendaryCloses()
         {
-            if (File.Exists(Path.Combine(LegendaryLauncher.ConfigPath, "installed.json.lock")))
+            var installedLockPath = Path.Combine(LegendaryLauncher.ConfigPath, "installed.json.lock");
+            if (File.Exists(installedLockPath) && Helpers.IsFileLocked(installedLockPath))
             {
                 await Task.Delay(1000);
                 await WaitUntilLegendaryCloses();