Add new err msg - thx darnn :)

Fix  #6878

LanguageBaseEnglish.xml

@@ -1542,6 +1542,7 @@ To use an API key, go to "Options -> Settings -> Tools" to enter your Goog
     <LoadedEmptyOrShort>Loaded empty or very short subtitle {0}</LoadedEmptyOrShort>
     <FileIsEmptyOrShort>File is empty or very short!</FileIsEmptyOrShort>
     <FileNotFound>File not found: {0}</FileNotFound>
+    <FileLocked>Unable to open file as it is in use by another program: {0}</FileLocked>
     <SavedSubtitleX>Saved subtitle {0}</SavedSubtitleX>
     <SavedOriginalSubtitleX>Saved original subtitle {0}</SavedOriginalSubtitleX>
     <FileOnDiskModified>File on disk modified</FileOnDiskModified>

src/libse/Common/FileUtil.cs

@@ -609,5 +609,22 @@ namespace Nikse.SubtitleEdit.Core.Common
                 return validator.IsValid;
             }
         }
+
+        public static bool IsFileLocked(string fileName)
+        {
+            try
+            {
+                using (var stream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.None))
+                {
+                    stream.Close();
+                }
+            }
+            catch (IOException)
+            {
+                return true;
+            }
+
+            return false;
+        }
     }
 }

src/ui/Forms/Main.cs

@@ -2756,6 +2756,12 @@ namespace Nikse.SubtitleEdit.Forms
                 return;
             }
 
+            if (FileUtil.IsFileLocked(fileName))
+            {
+                MessageBox.Show(string.Format(_language.FileLocked, fileName));
+                return;
+            }
+
             _lastAutoSave = DateTime.UtcNow.Ticks;
             bool videoFileLoaded = false;
             _formatManuallyChanged = false;

src/ui/Logic/Language.cs

@@ -1447,6 +1447,7 @@ namespace Nikse.SubtitleEdit.Logic
                 LoadedEmptyOrShort = "Loaded empty or very short subtitle {0}",
                 FileIsEmptyOrShort = "File is empty or very short!",
                 FileNotFound = "File not found: {0}",
+                FileLocked = "Unable to open file as it is in use by another program: {0}",
                 SavedSubtitleX = "Saved subtitle {0}",
                 SavedOriginalSubtitleX = "Saved original subtitle {0}",
                 FileOnDiskModified = "File on disk modified",

src/ui/Logic/LanguageDeserializer.cs

@@ -3190,6 +3190,9 @@ namespace Nikse.SubtitleEdit.Logic
                 case "Main/FileNotFound":
                     language.Main.FileNotFound = reader.Value;
                     break;
+                case "Main/FileLocked":
+                    language.Main.FileLocked = reader.Value;
+                    break;
                 case "Main/SavedSubtitleX":
                     language.Main.SavedSubtitleX = reader.Value;
                     break;

src/ui/Logic/LanguageStructure.cs

@@ -1307,6 +1307,7 @@ namespace Nikse.SubtitleEdit.Logic
             public string LoadedEmptyOrShort { get; set; }
             public string FileIsEmptyOrShort { get; set; }
             public string FileNotFound { get; set; }
+            public string FileLocked { get; set; }
             public string SavedSubtitleX { get; set; }
             public string SavedOriginalSubtitleX { get; set; }
             public string FileOnDiskModified { get; set; }