build: fix filesystem::path to string conversion

Change-Id: I2c3a9f626ca56d63c239f2afc5d9ed71db6f631d
diff --git a/src/connectionmanager.cpp b/src/connectionmanager.cpp
index dafd338..2b6e544 100644
--- a/src/connectionmanager.cpp
+++ b/src/connectionmanager.cpp
@@ -1345,9 +1345,9 @@
 {
     std::lock_guard<std::mutex> lock(messageMutex_);
     auto path = config_->cachePath / "treatedMessages";
-    treatedMessages_ = loadIdList<std::string>(path);
+    treatedMessages_ = loadIdList<std::string>(path.string());
     if (treatedMessages_.empty()) {
-        auto messages = loadIdList(path);
+        auto messages = loadIdList(path.string());
         for (const auto& m : messages)
             treatedMessages_.emplace(to_hex_string(m));
     }