theme: preserve cursor when clearing multiple lines of input.

After clearing, we want to have the cursor at the beginning of the current line.

Author: grunweg

src/theme.rs

@@ -839,7 +839,13 @@ impl<'a> TermThemeRenderer<'a> {
         })
     }
 
+    /// Clear the current theme.
+    ///
+    /// Position the cursor at the beginning of the current line.
     pub fn clear(&mut self) -> io::Result<()> {
+        // We must clear the current line first: `clear_last_lines` places the cursor on the first deleted line,
+        // whereas we want to have it on the current line.
+        self.term.clear_line()?;
         self.term
             .clear_last_lines(self.height + self.prompt_height)?;
         self.height = 0;