patch 8.1.1498: ":write" increments b:changedtick even though nothing changed

Problem:    ":write" increments b:changedtick even though nothing changed.
            (Daniel Hahler)
Solution:   Only increment b:changedtick if the modified flag is reset.
diff --git a/src/fileio.c b/src/fileio.c
index d746298..e6fb6bf 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4908,8 +4908,8 @@
 	    && !write_info.bw_conv_error
 	    && (overwriting || vim_strchr(p_cpo, CPO_PLUS) != NULL))
     {
-	unchanged(buf, TRUE);
-	/* b:changedtick is always incremented in unchanged() but that
+	unchanged(buf, TRUE, FALSE);
+	/* b:changedtick is may be incremented in unchanged() but that
 	 * should not trigger a TextChanged event. */
 	if (buf->b_last_changedtick + 1 == CHANGEDTICK(buf))
 	    buf->b_last_changedtick = CHANGEDTICK(buf);
@@ -7081,7 +7081,7 @@
 	    else if (buf == curbuf)  /* "buf" still valid */
 	    {
 		/* Mark the buffer as unmodified and free undo info. */
-		unchanged(buf, TRUE);
+		unchanged(buf, TRUE, TRUE);
 		if ((flags & READ_KEEP_UNDO) == 0)
 		{
 		    u_blockfree(buf);