Listing build targets does not work until project is done compiling

[harpocrates]

Steps to repro:

1. initialize a BSP connection with Bloop
2. check that workspace/buildTargets is correctly returning targets
3. trigger a long compilation with buildTarget/compile
4. as soon as the compilation starts, try to run workspace/buildTargets again and observe that it does not return results until the compilation is done

My expectation is that something like workspace/buildTargets should not be affected by the outcome of the compilation, so should always be able to run.