LibRegex: Merge inverse string table mappings separately

Author: https://github.com/alimpfard
Commit: 69050da929
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4246

Libraries/LibRegex/RegexOptimizer.cpp

@@ -999,11 +999,10 @@ void Optimizer::append_alternation(ByteCode& target, Span<ByteCode> alternatives
     if (alternatives.size() == 0)
         return;
 
-    target.merge_string_tables_from(alternatives);
-
     if (alternatives.size() == 1)
         return target.extend(move(alternatives[0]));
 
+    target.merge_string_tables_from(alternatives);
     if (all_of(alternatives, [](auto& x) { return x.is_empty(); }))
         return;