patch 8.2.2569: 'fillchars' "stl" and "stlnc" items must be single byte

Problem:    'fillchars' "stl" and "stlnc" items must be single byte.
Solution:   Accept multi-byte characters. (Christian Wellenbrock, Yegappan
            Lakshmanan, closes #7927)
diff --git a/src/screen.c b/src/screen.c
index ce4ab11..84951c5 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -266,7 +266,7 @@
     empty = (fdc == 1) ? 0 : 1;
 
     // If the column is too narrow, we start at the lowest level that
-    // fits and use numbers to indicated the depth.
+    // fits and use numbers to indicate the depth.
     first_level = level - fdc - closed + 1 + empty;
     if (first_level < 1)
 	first_level = 1;