patch 8.1.0989: various small code ugliness

Problem:    Various small code ugliness.
Solution:   Remove pointless NULL checks. Fix function calls. Fix typos.
            (Dominique Pelle, closes #4060)
diff --git a/src/ops.c b/src/ops.c
index c5e2be5..02c985a 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -5402,7 +5402,7 @@
     linenr_T		amount = Prenum1;
 
    // do_addsub() might trigger re-evaluation of 'foldexpr' halfway, when the
-   // buffer is not completly updated yet. Postpone updating folds until before
+   // buffer is not completely updated yet. Postpone updating folds until before
    // the call to changed_lines().
 #ifdef FEAT_FOLDING
    disable_fold_update++;