fix os judgement

Author: Mikachu2333

lib/xy.h

@@ -800,15 +800,16 @@ _xy_os_home ()
  */
 static char *
 _xy_win_get_documents_dir() {
-#ifdef xy_on_windows
-  char documents_path[MAX_PATH];
-  HRESULT result = SHGetFolderPathA(NULL, CSIDL_MYDOCUMENTS, NULL,
-                                    SHGFP_TYPE_CURRENT, documents_path);
+  if (xy_on_windows)
+  {
+    char documents_path[MAX_PATH];
+    HRESULT result = SHGetFolderPathA(NULL, CSIDL_MYDOCUMENTS, NULL,
+                                      SHGFP_TYPE_CURRENT, documents_path);
 
-  if (SUCCEEDED(result)) {
-    return xy_strdup(documents_path);
+    if (SUCCEEDED(result)) {
+      return xy_strdup(documents_path);
+    }
   }
-#endif
 
   return xy_2pathjoin(xy_os_home, "Documents");
 }