repl: preserve the cursor when redisplaying the prompt on SIGCONT
repl: preserve the cursor when redisplaying the prompt on SIGCONT

Otherwise the cursor position was being reset to 0, even when there was
already part of a line, which was strange.

Part of #3295.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node