msi: Only read an internal package if the file to install is compressed.

dlls/msi/files.c

@@ -573,8 +573,11 @@ static UINT load_media_info(MSIPACKAGE *package, MSIFILE *file, struct media_inf
         mi->first_volume = strdupW(mi->volume_label);
 
     source_dir = msi_dup_property(package, cszSourceDir);
+    lstrcpyW(mi->source, source_dir);
 
-    if (mi->cabinet && mi->cabinet[0] == '#')
+    if (file->IsCompressed && mi->cabinet)
+    {
+        if (mi->cabinet[0] == '#')
         {
             r = writeout_cabinet_stream(package, &mi->cabinet[1], mi->source);
             if (r != ERROR_SUCCESS)
@@ -584,11 +587,6 @@ static UINT load_media_info(MSIPACKAGE *package, MSIFILE *file, struct media_inf
             }
         }
         else
-    {
-        lstrcpyW(mi->source, source_dir);
-
-
-        if (mi->cabinet)
             lstrcatW(mi->source, mi->cabinet);
     }