Weak EMP grenades actually strong

[cyberillithid]

Description of issue

Low-yield EMP grenades actually detonate as normal EMP grenades first and then as a low-yield one, thus making them actually a bit higher-yield than normal-yield.

First reported by @sirleatherflute.

Difference between expected and actual behavior

Expected: Low-yield would have lower yield than normal
Actual: Technically it's even higher for double EMP burst (normal then lower).

Steps to reproduce

1. Obtain low-yield EMP grenade
2. Detonate it
3. Observe 10m radius of EMP effects

Specific information for locating

In code\game\objects\items\weapons\grenades\emgrenade.dm:

/obj/item/grenade/empgrenade/low_yield/detonate() calls ..(), which obviously resolves as /obj/item/grenade/empgrenade/detonate().

Length of time in which bug has been known to occur

I'd guess it has been occuring since well before #2778 which created a low-yield EMP grenades box -- with this ..()-call unmodified since then.

Client version, Server revision & Game ID

Reproducible on locally run Nebula:stable, e.g.:

Server Revision: 0afd441424308c5a097579a2319777f7b6b5c801 - stable - 
Game ID: cqn-cxB0
Current map: Tradeship Ocelot Alpha

Issue bingo

• Issue could be reproduced at least once
• Issue could be reproduced by different players
• Issue could be reproduced in multiple rounds
• Issue happened in a recent (less than 7 days ago) round
• Couldn't find an existing issue about this