[lldb] Save the edited line before clearing it in Editline::PrintAsync (#84154)

If the `m_editor_status` is `EditorStatus::Editing`, PrintAsync clears
the currently edited line. In some situations, the edited line is not
saved. After the stream flushes, PrintAsync tries to display the unsaved
line, causing the loss of the edited line.

The issue arose while I was debugging REPRLRun in
[Fuzzilli](https://github.com/googleprojectzero/fuzzilli). I started
LLDB and attempted to set a breakpoint in libreprl-posix.c. I entered
`breakpoint set -f lib` and used the "tab" key for command completion.
After completion, the edited line was flushed, leaving a blank line.