LibRegex: Remove orphaned save points in nested LookAhead

Author: https://github.com/mikiubo
Commit: c85df78c4c
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3949
Reviewed-by: https://github.com/alimpfard

Tests/LibRegex/Regex.cpp

@@ -738,6 +738,9 @@ TEST_CASE(ECMA262_match)
         // Optimizer bug, ignoring an enabled trailing 'invert' when comparing blocks, ladybird#3421.
         { "[^]*[^]"sv, "i"sv, true },
         { "xx|...|...."sv, "cd"sv, false },
+        // Tests nested lookahead with alternation - verifies proper save/restore stack cleanup
+        { "a(?=.(?=c)|b)b"sv, "ab"sv, true },
+        { "(?=)(?=\\d)"sv, "smart"sv, false },
     };
 
     for (auto& test : tests) {