Move SetSearchLabel definition to srchdlg.cxx
Set control foreground to red on failed search and reset on text input
modification.
For the find & replace dialog, use set_entry_error for the same.
Reset "not found" search label on modification of search term.

Change-Id: Ia89d2e8d3ca35e2c184d5b7048af8267b57f2c17
Reviewed-on: https://gerrit.libreoffice.org/70662
Tested-by: Jenkins
Reviewed-by: Heiko Tietze <tietze.heiko@gmail.com>
Tested-by: Heiko Tietze <tietze.heiko@gmail.com>
Reviewed-by: Jim Raykowski <raykowj@gmail.com>