patch 8.2.2945: some buffer related code is not tested

Problem:    Some buffer related code is not tested.
Solution:   Add a few more tests. (Yegappan Lakshmanan, closes #8320)
diff --git a/src/termlib.c b/src/termlib.c
index e05daae..7c845c5 100644
--- a/src/termlib.c
+++ b/src/termlib.c
@@ -591,7 +591,7 @@
     static char *
 _find(char *s, char *set)
 {
-    for(; *s; s++)
+    for (; *s; s++)
     {
 	char	*ptr = set;