This fixes https://bugs.winehq.org/show_bug.cgi?id=52094.
For reference, here's how current_modref is being passed around (before this patch):
```mermaid graph TB fii["fixup_imports_ilonly<br><em style='color:#ff0'>(directly sets current_modref)</em>"] fi["fixup_imports<br><em style='color:#ff0'>(directly sets current_modref)</em>"] pa["process_attach<br><em style='color:#ff0'>(directly sets current_modref)</em>"] ld[load_dll] id["import_dll<br><em style='color:#0f0'>(directly uses current_modref)</em>"] bin["build_import_name<br><em style='color:#0f0'>(directly uses current_modref)</em>"] foe["find_ordinal_export<br><em style='color:#0f0'>(uses current_modref for relay)</em>"] ffe["find_forwarded_export<br><em style='color:#0f0'>(directly uses current_modref)</em>"] fne[find_named_export] MI[MODULE_InitDLL] fii --> ld fi --> id pa --> MI -.-> DllMain id --> bin id --> ld id --> foe id --> fne --> foe --> ffe --> foe ffe --> fne ffe --> bin style DllMain color:red; ```
-- v15: ntdll: Remove superflous NULL check for importer. ntdll: Properly track refcount on dynamic imports of export forwarders. ntdll: Explicitly ignore dynamic (GetProcAddress) importers as relay/snoop user module. ntdll: Eagerly call process_attach() on dynamic imports of export forwarders. ntdll: Properly track refcount on static imports of export forwarders. ntdll: Register module dependency for export forwarders regardless of whether the dependency is already loaded. ntdll: Don't re-add a module dependency if it already exists. ntdll: Sink module dependency registration towards the end of the