fix: 修复 7 个编译警告

- CA2022: QQPinyinQcelImporter 使用 ReadExactly 替代 Read
- CS8604: SplitFileWindow/MergeWLWindow 添加 null 防护

Author: studyzy

src/ImeWlConverter.Formats/QQPinyinQcel/QQPinyinQcelImporter.cs

@@ -114,9 +114,9 @@ protected override IReadOnlyList<WordEntry> ParseBinary(Stream input, Cancellati
 
             // Skip 2 bytes (unknown short) + 4 bytes (unknown int)
             var skip1 = new byte[2];
-            fs.Read(skip1, 0, 2);
+            fs.ReadExactly(skip1, 0, 2);
             var skip2 = new byte[4];
-            fs.Read(skip2, 0, 4);
+            fs.ReadExactly(skip2, 0, 4);
 
             results.Add(new WordEntry
             {
@@ -128,7 +128,7 @@ protected override IReadOnlyList<WordEntry> ParseBinary(Stream input, Cancellati
 
             // Skip trailing 6 bytes per entry
             var trailing = new byte[6];
-            fs.Read(trailing, 0, 6);
+            fs.ReadExactly(trailing, 0, 6);
         }
 
         return results;

src/ImeWlConverterMac/Views/MergeWLWindow.axaml.cs

@@ -101,7 +101,7 @@ private async void BtnMergeWL_Click(object? sender, RoutedEventArgs e)
 
     private async void PerformMerge()
     {
-        var mainWL = FileOperationHelper.ReadFile(txbMainWLFile.Text);
+        var mainWL = FileOperationHelper.ReadFile(txbMainWLFile.Text ?? "");
         var mainDict = ConvertTxt2Dictionary(mainWL);
         var userFiles = (txbUserWLFiles.Text ?? "").Split('|');
 

src/ImeWlConverterMac/Views/SplitFileWindow.axaml.cs

@@ -82,8 +82,9 @@ await Task.Run(() =>
 
     private void SplitFileByLine(int maxLine)
     {
-        var encoding = FileOperationHelper.GetEncodingType(txbFilePath.Text);
-        var str = FileOperationHelper.ReadFile(txbFilePath.Text, encoding);
+        var filePath = txbFilePath.Text ?? "";
+        var encoding = FileOperationHelper.GetEncodingType(filePath);
+        var str = FileOperationHelper.ReadFile(filePath, encoding);
 
         var splitLineChar = "\r\n";
         if (str.IndexOf(splitLineChar) < 0)
@@ -127,7 +128,8 @@ private void SplitFileByLine(int maxLine)
 
     private void SplitFileBySize(int maxSize)
     {
-        var encoding = FileOperationHelper.GetEncodingType(txbFilePath.Text);
+        var filePath = txbFilePath.Text ?? "";
+        var encoding = FileOperationHelper.GetEncodingType(filePath);
         var fileIndex = 1;
         var size = (maxSize - 10) * 1024; // 10K的Buffer
 
@@ -192,8 +194,9 @@ private bool ReadToNextLine(FileStream fs)
     private void SplitFileByLength(int length)
     {
         length = length - 100; // 100个字的Buffer
-        var encoding = FileOperationHelper.GetEncodingType(txbFilePath.Text);
-        var str = FileOperationHelper.ReadFile(txbFilePath.Text, encoding);
+        var filePath = txbFilePath.Text ?? "";
+        var encoding = FileOperationHelper.GetEncodingType(filePath);
+        var str = FileOperationHelper.ReadFile(filePath, encoding);
         var fileIndex = 1;
 
         do