Merge bitcoin/bitcoin#22591: Util: error if settings json exists, but is unreadable

2b07126 error if settings.json exists, but is unreadable (Tyler Chambers)

Pull request description:

  If settings.json exists, but is unreadable, we should error instead of overwriting.

  Fixes #22571

ACKs for top commit:
  Zero-1729:
    tACK 2b07126
  ShaMan239:
    tACK 2b07126
  prayank23:
    tACK bitcoin/bitcoin@2b07126
  ryanofsky:
    Code review ACK 2b07126. Thanks for the fix! Note that PR   #379 will change the appearance of dialogs shown in screenshots above. So it could be interesting to test the two PRs together (but current testing seems more than sufficient)
  theStack:
    ACK 2b07126 📁

Tree-SHA512: 6f7f96ce8a13213d0335198a2245d127264495c877105058d1503252435915b332a6e55068ac21088f4c0c017d564689f4956213328d5bdee81d73711efc5511

Author: MarcoFalke

src/util/settings.cpp

@@ -60,9 +60,15 @@ bool ReadSettings(const fs::path& path, std::map<std::string, SettingsValue>& va
     values.clear();
     errors.clear();
 
+    // Ok for file to not exist
+    if (!fs::exists(path)) return true;
+
     fsbridge::ifstream file;
     file.open(path);
-    if (!file.is_open()) return true; // Ok for file not to exist.
+    if (!file.is_open()) {
+      errors.emplace_back(strprintf("%s. Please check permissions.", path.string()));
+      return false;
+    }
 
     SettingsValue in;
     if (!in.read(std::string{std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>()})) {