Just add one extra character in the regexp:

    while (s/<([^>]*)\s+          # Open tag, name and assorted crud.
             ($NMTEXT)="([^ >]*)" # Attribute and value
             (|\s+[^>]*)?\s+      # Optional assorted crud
             \2="([^ >]*)"        # Repeated attribute and value
            /<$1 $2="$3,$5"$4/gx) {
    }
[download]

Notice the "Optional assorted crud" part.

Abigail