message: [gui] Simplify SourceFileWindowDelegate::WindowDelegateDraw
  instead of printf-ing into a buffer, and them using that buffer as a
  format string, simply use the appropriate indirect format string.
  This also fixes a -Wformat-truncation warning with gcc.
diff: @@ -3929,12 +3929,10 @@ public:
  m_debugger.GetSourceManager().GetFile(m_sc.line_entry.file);
  if (m_file_sp) {
  const size_t num_lines = m_file_sp->GetNumLines();
  - int m_line_width = 1;
  + m_line_width = 1;
  for (size_t n = num_lines; n >= 10; n = n / 10)
  ++m_line_width;
  - snprintf(m_line_format, sizeof(m_line_format), " %%%iu ",
  - m_line_width);
  if (num_lines < num_visible_lines ||
  m_selected_line < num_visible_lines)
  m_first_visible_line = 0;
  @@ -4051,7 +4049,7 @@ public:
  if (bp_attr)
  window.AttributeOn(bp_attr);
  - window.Printf(m_line_format, curr_line + 1);
  + window.Printf(" %*u ", m_line_width, curr_line + 1);
  if (bp_attr)
  window.AttributeOff(bp_attr);
  @@ -4477,7 +4475,6 @@ protected:
  AddressRange m_disassembly_range;
  StreamString m_title;
  lldb::user_id_t m_tid;
  - char m_line_format[8];
  int m_line_width;
  uint32_t m_selected_line; // The selected line
  uint32_t m_pc_line; // The line with the PC
  