msi: Don't check for a cabinet's existence if it's embedded in the package.

dlls/msi/files.c

@@ -637,7 +637,8 @@ static UINT ready_media(MSIPACKAGE *package, MSIFILE *file, struct media_info *m
         }
     }
 
-    if (file->IsCompressed && mi->cabinet &&
+    if (file->IsCompressed &&
+        mi->cabinet && mi->cabinet[0] != '#' &&
         GetFileAttributesW(mi->cabinet) == INVALID_FILE_ATTRIBUTES)
     {
         ERR("Cabinet not found: %s\n", debugstr_w(mi->cabinet));