Fix find_XXX(...) functions
Fix find_XXX(...) functions

Allow them to pick the first index if no index is provided.

Signed-off-by: Chris Harris <a361e89d1eba6c570561222d75facbbf7aaeeafe@kitware.com>

OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz