patch 8.2.4929: off-by-one error in in statusline item

Problem:    Off-by-one error in in statusline item.
Solution:   Subtrace one less. (closes #10394, closes #5599)
diff --git a/src/buffer.c b/src/buffer.c
index 17b1493..35711f5 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4446,7 +4446,8 @@
 		// correct the start of the items for the truncation
 		for (l = stl_groupitem[groupdepth] + 1; l < curitem; l++)
 		{
-		    stl_items[l].stl_start -= n;
+		    // Minus one for the leading '<' added above.
+		    stl_items[l].stl_start -= n - 1;
 		    if (stl_items[l].stl_start < t)
 			stl_items[l].stl_start = t;
 		}