Add INFO comment when DB not scaned

[jihuayu]

I noticed that many people are unaware that they need to run dbsize scan first in order to obtain the "keys num" information.

So I have added the logic: when dbsize scan has not been executed, the INFO command will display a warning to remind the user to run the dbsize scan command.

WARN: DB not scan, run `dbsize scan` command first.
db0:keys=0,expires=0,avg_ttl=0,expired=0

[tisonkun]

Thank you!

[sonarcloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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