patch 8.2.0502: Vim9: some code is not tested

Problem:    Vim9: some code is not tested.
Solution:   Add more tests.  Fix uncovered problems.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index bc3cccc..4b0645a 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -277,7 +277,7 @@
     p = skipwhite(p);
     delim = (delim_optional && vim_isIDc(*p)) ? ' ' : *p++;
     *search_delim = delim;
-    end = skip_regexp(p, delim, p_magic, NULL);
+    end = skip_regexp(p, delim, p_magic);
 
     use_last_pat = end == p && *end == delim;