Fix empty callback for hr adjustment

[PabstMirror]

Fix #3526
Same issue as #3384

[grester]

I know this has been closed but I'd like to point out that I'm not sure if this is indeed a bug or instead mod conflict. I say this because I have some simple missions where this error doesn't show up but I have some other missions with more scripts where the error does show up for all injections not just morphine. Just a heads up.

[commy2]

Would be helpful to know which mod or mission causes the conflict.

[grester]

I have yet had success in tracking down what's causing it in my case. However I'd like to point out though that despite the error the injection is still applied successfully and it takes effect on both pulse and pressure. I've been editing my mission with only ACE, CBA and Eden Enchanced (this one isn't culprit as a simple mission done with it causes no problem). It's either a module or some disruptive script.

[PabstMirror]

I have seen this with just CBA/ACE. I'm fairly sure it's a BIS thing.

x = missionNamespace getVariable ""
typeOf x = "EmptyDetector"

There are no medications that have a real callback, they all use hrCallback = "";
We could use something more explicit like `hrCallback = "#none", but I think this fix is good enough.