Fix crashes coming from new memorial function

Call the function like this:
```
g->u.add_memorial_log("Installed %s", bionic.c_str());
```
turns to this:
```
vsnprintf(buff, sizeof(buff), "Installed %s", ...);
```
which crashes as vsnprintf expects something for %s, but here is no further argument.

Or to this:
```
vsnprintf(buff, sizeof(buff), bionic.c_str(), ...);
```
which has the wrong message.

Can be seen when installing a bionic.