cli: fix escape buffer overflow check

This commit add escape buffer overflow check when cli receive
escape sequence(cursor position response). escape buffer size
is 8 bytes, the last byte used to store string end symbol '\0'.
So the longest string escape buffer can save is 7 bytes. But in
some console or tool, the cursor position response sequence is
more then 7 bytes, and escap buffer will overflow. This patch
fix it.

Signed-off-by: Zhilong Wubin <zhilong.wb@alibaba-inc.com>