patch 8.2.4656: Vim9: can't use item from "import autoload" with autoload dir

Problem:    Vim9: can't use items from "import autoload" with autoload
            directory name.
Solution:   Let sn_autoload_prefix overrule sn_import_autoload.
            (closes #10054)
diff --git a/src/vim9instr.c b/src/vim9instr.c
index ae828cb..ab52d4c 100644
--- a/src/vim9instr.c
+++ b/src/vim9instr.c
@@ -1932,7 +1932,9 @@
 		isntype_T isn_type = ISN_STORES;
 
 		if (SCRIPT_ID_VALID(scriptvar_sid)
-			 && SCRIPT_ITEM(scriptvar_sid)->sn_import_autoload)
+			 && SCRIPT_ITEM(scriptvar_sid)->sn_import_autoload
+			 && SCRIPT_ITEM(scriptvar_sid)->sn_autoload_prefix
+								       == NULL)
 		{
 		    // "import autoload './dir/script.vim'" - load script first
 		    if (generate_SOURCE(cctx, scriptvar_sid) == FAIL)