patch 9.1.0759: screenpos() may return invalid position

Problem:  screenpos() may return invalid position
          after switching buffers (Greg Hurrell)
Solution: reset w_leftcol if wrapping has been set
          after copying wrap option

fixes: #15792
closes: #15803

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/option.c

@@ -6737,6 +6737,11 @@ win_copy_options(win_T *wp_from, win_T *wp_to)
     void
 after_copy_winopt(win_T *wp)
 {
+    // Set w_leftcol or w_skipcol to zero.
+    if (wp->w_p_wrap)
+	wp->w_leftcol = 0;
+    else
+	wp->w_skipcol = 0;
 #ifdef FEAT_LINEBREAK
     briopt_check(wp);
 #endif