[BUG] Issue with clinical charts on Study View when multiple studies are combined

[sowmiyaa-kumar]

When combining multiple studies, there are two issues that may arise with the clinical sample attribute charts when filtering down to a study which do not have the attributes being displayed:

1. They disappear.
2. They show the counts of the number of patients, albeit being a sample attribute.

To Reproduce
Steps to reproduce the behavior of the first part of the error:

1. Go to 'https://www.cbioportal.org/study/summary?id=mixed_pipseq_2017%2Call_stjude_2016'.
2. Click on 'Charts' and Deselect All.
3. Add only sample-specific charts such as 'Sample Class' and 'Sample Timepoint'.
4. Then add the 'Cancer Studies' Chart.
5. Filter down to only the samples in the 'all_stjude_2016' study.
6. The charts in 'Sample Class' and 'Sample Timepoint' will disappear.

Steps to reproduce the behavior of the second part of the error:

1. Follow the steps 1-6 above.
2. Add a patient-specific attribute chart such as 'Number of Samples Per Patient'.
3. The charts for 'Sample Class' and 'Sample Timepoint' will reappear but the count is the number of patients, rather than the number of samples.

Expected behavior
The clinical sample pie charts should show NA values with the sample count of the study that is being filtered on.

Screenshots