patch 9.0.1603: display wrong if scrolling multiple lines with 'smoothscroll'

Problem:    Display wrong when scrolling multiple lines with 'smoothscroll'
            set.
Solution:   Redraw when w_skipcol changed. (closes #12477, closes #12468)

src/move.c

@@ -1785,6 +1785,7 @@ scrollup(
 	int	    width2 = width1 + curwin_col_off2();
 	int	    size = 0;
 	linenr_T    prev_topline = curwin->w_topline;
+	colnr_T	    prev_skipcol = curwin->w_skipcol;
 
 	if (do_sms)
 	    size = linetabsize(curwin, curwin->w_topline);
@@ -1847,8 +1848,9 @@ scrollup(
 	    }
 	}
 
-	if (curwin->w_topline == prev_topline)
+	if (curwin->w_topline == prev_topline
-	    // need to redraw even though w_topline didn't change
+		|| curwin->w_skipcol != prev_skipcol)
+	    // need to redraw because wl_size of the topline may now be invalid
 	    redraw_later(UPD_NOT_VALID);
     }
     else

src/testdir/dumps/Test_smooth_multi_skipcol_1.dump

@@ -0,0 +1,10 @@
+> +8&#ffffff0@39
+| +0&&@39
+|a@39
+@10| @29
+@40
+@40
+@40
+@40
+|b@2| @36
+@22|1|,|0|-|1| @8|T|o|p| 

src/testdir/dumps/Test_smooth_multi_skipcol_2.dump

@@ -0,0 +1,10 @@
+|<+0#4040ff13#ffffff0@2|a+8#0000000&@5>a| @29
+| +0&&@39
+@40
+@40
+@40
+|b@2| @36
+|c@2| @36
+|~+0#4040ff13&| @38
+|~| @38
+| +0#0000000&@21|3|,|5|0| @9|B|o|t| 

src/testdir/test_scroll_opt.vim

@@ -792,4 +792,26 @@ func Test_smoothscroll_incsearch()
   call StopVimInTerminal(buf)
 endfunc
 
+" Test scrolling multiple lines and stopping at non-zero skipcol.
+func Test_smoothscroll_multi_skipcol()
+  CheckScreendump
+
+  let lines =<< trim END
+      setlocal cursorline scrolloff=0 smoothscroll
+      call setline(1, repeat([''], 9))
+      call setline(3, repeat('a', 50))
+      call setline(8, 'bbb')
+      call setline(9, 'ccc')
+      redraw
+  END
+  call writefile(lines, 'XSmoothMultiSkipcol', 'D')
+  let buf = RunVimInTerminal('-S XSmoothMultiSkipcol', #{rows: 10, cols: 40})
+  call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_1', {})
+
+  call term_sendkeys(buf, "3\<C-E>")
+  call VerifyScreenDump(buf, 'Test_smooth_multi_skipcol_2', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1603,
 /**/
     1602,
 /**/