patch 9.1.1319: Various typos in the code, issue with test_inst_complete.vim

Problem:  Various typos in the code, redundant and strange use of
          :execute in test_ins_complete.vim (after 9.1.1315).
Solution: Fix typos in the code and in the documentation, use the
          executed command directly (zeertzjq).

closes: #17143

Co-authored-by: Christ van Willegen <cvwillegen@gmail.com>
Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ops.c b/src/ops.c
index 0e3711e..b4b59de 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -248,11 +248,11 @@
     int	sum = 0;
     int	i;
 
-    // Perform the summation for indeces within the actual array.
+    // Perform the summation for indices within the actual array.
     for (i = 1; i <= index && i <= vts_array[0]; i++)
 	sum += vts_array[i];
 
-    // Add topstops whose indeces exceed the actual array.
+    // Add tabstops whose indices exceed the actual array.
     if (i <= index)
 	sum += vts_array[vts_array[0]] * (index - vts_array[0]);