Fix app can not restart after an unexpected exit during the apply releases

src/Squirrel/UpdateManager.ApplyReleases.cs

@@ -308,13 +308,22 @@ Task<string> installPackageToAppDir(UpdateInfo updateInfo, ReleaseEntry release,
 
                     target.Create();
 
+                    // Create the .not-finished file before extraction is started
+                    var notFinishedFilePath = Path.Combine(target.FullName, ".not-finished");
+                    File.WriteAllText(notFinishedFilePath, "");
+
                     this.Log().Info("Writing files to app directory: {0}", target.FullName);
                     await ReleasePackage.ExtractZipForInstall(
                         Path.Combine(updateInfo.PackageDirectory, release.Filename),
                         target.FullName,
                         rootAppDirectory,
                         progressCallback);
 
+                    // Delete the .not-finished file after extraction is completed
+                    if (File.Exists(notFinishedFilePath)) {
+                        File.Delete(notFinishedFilePath);
+                    }
+
                     return target.FullName;
                 });
             }

src/StubExecutable/StubExecutable.cpp

@@ -8,6 +8,11 @@
 
 using namespace std;
 
+bool FileExists(const std::wstring& filePath) {
+    DWORD fileAttributes = GetFileAttributes(filePath.c_str());
+    return (fileAttributes != INVALID_FILE_ATTRIBUTES) && !(fileAttributes & FILE_ATTRIBUTE_DIRECTORY);
+}
+
 wchar_t* FindRootAppDir() 
 {
 	wchar_t* ourDirectory = new wchar_t[MAX_PATH];
@@ -67,6 +72,13 @@ std::wstring FindLatestAppDir()
 
 		version::Semver200_version thisVer(s);
 
+		// Skip the directory which contains a .not-finished file
+		std::wstring appFolder = fileInfo.cFileName;
+        std::wstring dirPath = ourDir.substr(0, ourDir.size() - 5) + appFolder;
+        if (FileExists(dirPath + L"\\.not-finished")) {
+            continue;
+        }
+
 		if (thisVer > acc) {
 			acc = thisVer;
 			acc_s = appVer;