patch 9.1.1973: some minor problems with clipboard provider code

patch 9.1.1973: some minor problems with clipboard provider code

Problem:  some minor problems with clipboard provider code
          (after v9.1.1972)
Solution: Fix minor issues (Foxe Chen)

- allow empty register type for paste function to mean automatic
- fix internal inc_clip_provider() and dec_clip_provider() functions not
  setting the pause count correctly
- don't call paste function when yanking

closes: #18909

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>