[filesystem] Return ResultPathAlreadyExists from CreateDirectory if path exists (#4224)

Returning success when the path already exists confuses games like Eastward which use this result in their save logic.

Closes https://github.com/eden-emulator/mirror/pull/10

Signed-off-by: crueter <crueter@eden-emu.dev>
Co-authored-by: Tom Pratt <tom.pratt@outlook.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4224
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

src/core/hle/service/filesystem/filesystem.cpp

@@ -108,7 +108,9 @@ Result VfsDirectoryServiceWrapper::DeleteFile(const std::string& path_) const {
 
 Result VfsDirectoryServiceWrapper::CreateDirectory(const std::string& path_) const {
     std::string path(Common::FS::SanitizePath(path_));
-
+    if (GetDirectoryRelativeWrapped(backing, path) != nullptr) {
+        return FileSys::ResultPathAlreadyExists;
+    }
     // NOTE: This is inaccurate behavior. CreateDirectory is not recursive.
     // CreateDirectory should return PathNotFound if the parent directory does not exist.
     // This is here temporarily in order to have UMM "work" in the meantime.