fix win32 warning in target.c

This was creating a warning during a win32 build:

```
dmc -c -Iroot;\dm\include -o   -cpp -DDM_TARGET_CPU_X86=1  target
target.c(152) : Warning 18: implied return of Target::critsecsize at closing '}' does not return value
```

It looked an awful lot like a compile error on first glance. This change avoids emit a warning. Not checked on all OS'es yet (need to run unittests). Will squash once validated.