patch 8.2.3914: various spelling mistakes in comments

Problem:    Various spelling mistakes in comments.
Solution:   Fix the mistakes. (Dominique Pellé, closes #9416)
diff --git a/src/gui_athena.c b/src/gui_athena.c
index f4aafcd..4da832b 100644
--- a/src/gui_athena.c
+++ b/src/gui_athena.c
@@ -216,7 +216,7 @@
     else if (value < 0)
 	value = 0;
 
-    // Update the bottom scrollbar an extra time (why is this needed??
+    // Update the bottom scrollbar an extra time (why is this needed??)
     if (sb->wp == NULL)		// Bottom scrollbar
 	gui_mch_set_scrollbar_thumb(sb, value, sb->size, sb->max);