util: Avoid buggy std::filesystem:::create_directories() call

Compiled with some libstdc++ versions (e.g., on Ubuntu 20.04)
std::filesystem:::create_directories() call fails to handle symbol links
properly.

src/util/system.cpp

@@ -443,14 +443,18 @@ const fs::path& ArgsManager::GetDataDir(bool net_specific) const
     } else {
         path = GetDefaultDataDir();
     }
-    if (net_specific)
-        path /= fs::PathFromString(BaseParams().DataDir());
 
-    if (fs::create_directories(path)) {
+    if (!fs::exists(path)) {
-        // This is the first run, create wallets subdirectory too
         fs::create_directories(path / "wallets");
     }
 
+    if (net_specific && !BaseParams().DataDir().empty()) {
+        path /= fs::PathFromString(BaseParams().DataDir());
+        if (!fs::exists(path)) {
+            fs::create_directories(path / "wallets");
+        }
+    }
+
     path = StripRedundantLastElementsOfPath(path);
     return path;
 }