programs/dll.inc: fix inverted Link result check in dll.Load

The inline dll.Link in this file returns the export-table pointer
(non-zero) on success and 0 if any import is unresolved - opposite
contract from the library-side dll.Link. The jnz .fail check after
dll.Link inverted that contract, so every successfully linked
library was reported as a failure, breaking all consumers of
programs/dll.inc.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

programs/dll.inc

@@ -18,7 +18,7 @@ proc dll.Load, import_table:dword
         jz      .fail
         stdcall dll.Link, eax, edx
         test    eax, eax
-        jnz     .fail
+        jz      .fail
         pop     esi
         add     esi, 8
         jmp     .next_lib