Add an initial libfuzzer based fuzzer for the admin console

Run the actual fuzzer like this:

./admin_fuzzer -max_len=16384 fuzzer/admin-data/

Change-Id: I5891df8033ff1837afce86775ee62447587f2f20
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/91504
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

fuzzer/Admin.cpp

@@ -0,0 +1,22 @@
+#include <iostream>
+
+#include "Admin.hpp"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    Admin& admin = Admin::instance();
+    auto handler = std::make_shared<AdminSocketHandler>(&admin);
+
+    std::string input(reinterpret_cast<const char*>(data), size);
+    std::stringstream ss(input);
+    std::string line;
+    while (std::getline(ss, line, '\n'))
+    {
+        std::vector<char> lineVector(line.data(), line.data() + line.size());
+        handler->handleMessage(lineVector);
+    }
+
+    return 0;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */