patch 9.2.0702: :windo and :tabdo create an extra window with 'winfixbuf'

patch 9.2.0702: :windo and :tabdo create an extra window with 'winfixbuf'

Problem:  With 'winfixbuf' set in the current window, :windo and :tabdo
          create an extra split window, even though they only visit
          existing windows/tabpages and don't change the current
          window's buffer (Collin Kennedy)
Solution: Skip the 'winfixbuf' escape in ex_listdo() for :windo and
          :tabdo (ShivaPriyanShanmuga)

fixes:  #14301
closes: #20600

Signed-off-by: ShivaPriyanShanmuga <pshanmugashiva@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>