Add exception to load_string_file when path does not exist

src/linkahead/utility.cpp

@@ -108,6 +108,10 @@ template <> auto getEnumValueFromName<Role>(const std::string &name) -> Role {
 auto load_string_file(const path &file_path) -> std::string {
   std::string result;
 
+  if (!exists(file_path)) {
+    throw std::runtime_error("File not found: " + file_path.string());
+  }
+
   // adapted from boost::filesystem::load_string_file, which was removed in 1.84
   std::ifstream file;
   file.exceptions(std::ios_base::failbit | std::ios_base::badbit);