Fix out of bound error in disk web

src/Disks/ObjectStorages/Web/WebObjectStorage.cpp

@@ -162,7 +162,22 @@ bool WebObjectStorage::exists(const std::string & path) const
 
     if (startsWith(it->first, path)
         || (it != files.begin() && startsWith(std::prev(it)->first, path)))
+    {
+        shared_lock.unlock();
+        std::unique_lock unique_lock(metadata_mutex);
+
+	/// The code relies on invariant that if this function returned true
+	/// the file exists in files.
+        /// In this case we have a directory which doesn't explicitly exists (like store/xxx/yyy)
+        ///                                                        ^^^^^
+	/// Adding it to the files
+        files.emplace(std::make_pair(path, FileData({.type = FileType::Directory})));
+
+        unique_lock.unlock();
+        shared_lock.lock();
+
         return true;
+    }
 
     return false;
 }