fix: optimization: PVS-Studio warning V815

The 'empty()' method is more efficient for checking if a string is empty compared to comparing it with an empty string literal.

The default constructor 'std::wstring()' is more efficient for creating an empty string compared to using a string literal.

The 'clear()' method is more efficient for clearing a std::wstring compared to assigning it an empty string literal.

Reported by: PVS-Studio
Signed-off-by: Vyacheslav Ivanov <islavaivanov76@gmail.com>

src/world/World.cpp

@@ -201,7 +201,7 @@ void World::deserialize(dynamic::Map* root) {
     generator = root->get("generator", generator);
     seed = root->get("seed", seed);
 
-    if (generator == "") {
+    if (generator.empty()) {
         generator = WorldGenerators::getDefaultGeneratorID();
     }
     if (auto verobj = root->map("version")) {