patch 9.1.0151: ml_get_buf_len() does not consider text properties

Problem:  ml_get_buf_len() does not consider text properties
          (zeertzj)
Solution: Store text length excluding text properties length
          in addition in the memline

related #14123
closes: #14133

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/structs.h b/src/structs.h
index 2c6f553..b3b3f6a 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -802,7 +802,8 @@
 #define ML_ALLOCATED	0x10	// ml_line_ptr is an allocated copy
     int		ml_flags;
 
-    colnr_T	ml_line_len;	// length of the cached line, including NUL
+    colnr_T	ml_line_len;	// length of the cached line + textproperties, including NUL
+    colnr_T	ml_line_textlen;// length of the cached line, including NUL
     linenr_T	ml_line_lnum;	// line number of cached line, 0 if not valid
     char_u	*ml_line_ptr;	// pointer to cached line