get rid of a warning when using newterm

newterm https://github.com/jeaye/ncurses-rs/blob/3aa22bc279e4929e3ab69d49f75a18eda3e431e9/src/lib.rs#L1023-L1029
CString::new https://doc.rust-lang.org/std/ffi/struct.CString.html#method.new

bubble up this newterm error

as suggested here: gyscos#778 (comment)

Co-authored-by: Alexandre Bury <alexandre.bury@gmail.com>

preserve original error in the panic report

otherwise, we'd not know why ncurses-rs newterm errored

directly include the variable name in the format! expression

as suggested here: gyscos#778 (comment)

Co-authored-by: Alexandre Bury <alexandre.bury@gmail.com>

cursive/src/backends/curses/n.rs

@@ -110,7 +110,10 @@ impl Backend {
             let path = CString::new(output_path).unwrap();
             unsafe { libc::fopen(path.as_ptr(), mode.as_ptr()) }
         };
-        ncurses::newterm(None, output, input);
+        ncurses::newterm(None, output, input).map_err(|e| {
+            io::Error::new(io::ErrorKind::Other, format!("could not call newterm: {e}"))
+        })?;
+
         // Enable keypad (like arrows)
         ncurses::keypad(ncurses::stdscr(), true);