vxfw.ScrollView: fix cursored line not displaying

[Justus2308]

Setting draw_cursor = true in vxfw.ScrollView would previously cause the cursored line to only display the cursor and not the actual content of the line.

Simple repro:

diff --git a/examples/scroll.zig b/examples/scroll.zig
index 0f92573..7b5e816 100644
--- a/examples/scroll.zig
+++ b/examples/scroll.zig
@@ -174,6 +174,7 @@ pub fn main() !void {
                         .buildFn = Model.widgetBuilder,
                     },
                 },
+                .draw_cursor = true,
             },
             // NOTE: This is not the actual content height, but rather an estimate. In reality
             //       you would want to do some calculations to keep this up to date and as close to

$ zig build example -Dexample=scroll