patch 8.1.2281: 'showbreak' cannot be set for one window

Problem:    'showbreak' cannot be set for one window.
Solution:   Make 'showbreak' global-local.
diff --git a/src/ops.c b/src/ops.c
index 42b0dcb..85e99f7 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -3636,9 +3636,11 @@
 	    {
 #ifdef FEAT_LINEBREAK
 		char_u * saved_sbr = p_sbr;
+		char_u * saved_w_sbr = curwin->w_p_sbr;
 
 		/* Make 'sbr' empty for a moment to get the correct size. */
 		p_sbr = empty_option;
+		curwin->w_p_sbr = empty_option;
 #endif
 		oparg.is_VIsual = 1;
 		oparg.block_mode = TRUE;
@@ -3647,6 +3649,7 @@
 					  &oparg.start_vcol, &oparg.end_vcol);
 #ifdef FEAT_LINEBREAK
 		p_sbr = saved_sbr;
+		curwin->w_p_sbr = saved_w_sbr;
 #endif
 		if (curwin->w_curswant == MAXCOL)
 		    oparg.end_vcol = MAXCOL;