Fix memory leak. 🤦

That's why I don't write C. 😄

This seems to fix issue #6 in single-threaded mode but sometimes throws “double
free or corruption (out)” in multi-threaded mode.

Bug: #6

src/zip.cpp

@@ -74,6 +74,7 @@ std::string read_file(const fs::path &filepath, std::string_view entry_path)
                            entry_path, filepath.string())};
             }
 
+            close_file(zipfile, filepath);
             return filecontents;
         }
         archive_read_data_skip(zipfile);