bug#21192: 25.0.50; search-replace of spaces erroneously touches newlines

[Dima Kogan]

Hi. The following is an erroneous behavior in a new build of emacs
(built from https://github.com/emacs-mirror/emacs/commit/bd3b426).

1. emacs -Q

2. Enter the following so the buffer looks like
--------------------
123
  abc
--------------------

3. M-%, ' ' -> '' (i.e. delete all spaces)

4. What should happen is that the ' ' before 'abc' should be removed.
Instead, the newline is removed also, so that I get a single line
'123abc'