get_cell_specimen_table LazyDoable does not work as intended.

**Describe the bug**
ophys plane dataset initialization sets cell specimens with nan traces to invalid using `_set_all_nan_traces_invalid`, but when using get_cell_specimen_table() function, nan trace cell specimens are changed to valid.

**To Reproduce**
> bod = BehaviorOphysDataset(plane_path, raw_path)
> bod._cell_specimen_table
> bod.get_cell_specimen_table()

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
Add any other context about the problem here.