patch 8.0.0524: folds messed up

Problem:    Folds are messed up when 'encodin' is "utf-8".
Solution:   Also set the fold character when it's not multi-byte.

Author: brammool

src/screen.c

@@ -2700,7 +2700,10 @@ fold_line(
                 ScreenLines[off + col] = 0x80; /* avoid storing zero */
 	    }
 	    else
+	    {
 		ScreenLinesUC[off + col] = 0;
+		ScreenLines[off + col] = fill_fold;
+	    }
 	    col++;
 	}
 	else

src/testdir/test_display.vim

@@ -54,6 +54,16 @@ func! Test_display_foldtext_mbyte()
         \ "  14                                    \u2502",
         \ ]
   call assert_equal(expect, lines)
+
+  set fillchars=fold:-,vert:\|
+  let lines=ScreenLines([1,3], winwidth(0)+1)
+  let expect=[
+        \ "  1                                     |",
+        \ "+ +-- 12 lines: 2". repeat("-", 23). "|",
+        \ "  14                                    |",
+        \ ]
+  call assert_equal(expect, lines)
+
   set foldtext& fillchars& foldmethod& fdc&
   bw!
 endfunc

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    524,
 /**/
     523,
 /**/