Return absolute path early in AbsPathForConfigVal

This prevents premature GetDataDir() calls, e.g., when config file is
not read yet.

src/util/system.cpp

@@ -1202,6 +1202,9 @@ int64_t GetStartupTime()
 
 fs::path AbsPathForConfigVal(const fs::path& path, bool net_specific)
 {
+    if (path.is_absolute()) {
+        return path;
+    }
     return fs::absolute(path, GetDataDir(net_specific));
 }