patch 9.2.0506: home_replace() function can be improved

patch 9.2.0506: home_replace() function can be improved

Problem:  home_replace() function can be improved
Solution: Refactor home_replace() to return the length of the string
          (John Marriott).

In addition:
- in function set_b0_fname() move ulen into the block where it is used.
- In function findswapname() rework logic around displaying "swap file
  already exists" dialogue so that literal message text is set once.

closes: #20249

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>