Fix typo that crashes UI when selecting slice timing (#710)

Reported-by: Nadza Dzinalija <n.dzinalija@amsterdamumc.nl>

src/halfpipe/ui/components/input/text.py

@@ -383,7 +383,7 @@ def _draw_option(self, i, y):
             if j == 0:
                 self.children[i].color = color
                 self.children[i].draw_at(y, x=x)
-                x = self.children[i].previousLength
+                x = self.children[i].previous_length
             else:
                 if color == self.highlight_color:
                     if self.cur_index is not None and i == self.cur_index and self.is_active: