Fix error when creating a temporary folder

Try to create the user's temporary directory, in case it doesn't already
exist. No test for this since it's in reaction to external system config
that's out of LOOT's control. Fixes #561.

src/backend/helpers/git_helper.cpp

@@ -166,6 +166,9 @@ namespace loot {
 
         fs::path tempPath = fs::temp_directory_path() / fs::unique_path();
 
+        // Create the temporary parent folder in case it doesn't already exist.
+        fs::create_directories(tempPath.parent_path());
+
         //Delete temporary folder in case it already exists.
         fs::remove_all(tempPath);