Fix regression when selection start is deleted

Ranges with start > end are invalid; we crash with "slice index starts at
10 but ends at 0".

src/reader.rs

@@ -1380,7 +1380,7 @@ fn paint_layout(&mut self, reason: &wstr) {
             let selection_color =
                 HighlightSpec::with_fg_bg(HighlightRole::selection, HighlightRole::selection);
             let end = std::cmp::min(selection.stop, colors.len());
-            for color in &mut colors[selection.start..end] {
+            for color in &mut colors[selection.start.min(end)..end] {
                 *color = selection_color;
             }
         }

tests/checks/tmux-bind.fish

@@ -19,3 +19,13 @@ isolated-tmux capture-pane -p
 # CHECK: prompt 0> begin
 # CHECK: echo 123
 # CHECK: end
+
+# regression test
+isolated-tmux send-keys C-c # not sure why we need to wait after this
+tmux-sleep
+isolated-tmux send-keys 'bind S begin-selection' Enter C-l
+tmux-sleep
+isolated-tmux send-keys 'echo one two threeS' C-u C-y
+tmux-sleep
+isolated-tmux capture-pane -p
+# CHECK: prompt 1> echo one two three