patch 9.1.0163: Calling STRLEN() to compute ml_line_textlen when not needed

Problem:  Calling STRLEN() to compute ml_line_textlen when not needed.
Solution: Use 0 when STRLEN() will be required and call STRLEN() later.
          (zeertzjq)

closes: #14155

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/change.c b/src/change.c
index 847c187..3af19b6 100644
--- a/src/change.c
+++ b/src/change.c
@@ -1364,7 +1364,7 @@
 	    mch_memmove(newp + newlen + 1, oldp + oldlen + 1,
 			       (size_t)curbuf->b_ml.ml_line_len - oldlen - 1);
 	curbuf->b_ml.ml_line_len -= count;
-	curbuf->b_ml.ml_line_textlen = (int)STRLEN(newp) + 1;
+	curbuf->b_ml.ml_line_textlen = 0;
     }
 #endif