Check number of scalars in properties panel update

When live updates are performed on data that contains multiple
scalars, the number of scalars can change in between updates.

Add in a safety check in the DataPropertiesPanel to account for
this. This prevents a crash.

Signed-off-by: Patrick Avery <patrick.avery@kitware.com>

Author: psavery

tomviz/DataPropertiesPanel.cxx

@@ -181,11 +181,15 @@ QList<ArrayInfo> DataPropertiesPanel::getArraysInfo(DataSource* dataSource)
 {
   QList<ArrayInfo> arraysInfo;
 
+  // If the number of scalar arrays has changed, reset the indexes.
+  auto scalars = dataSource->listScalars();
+  if (scalars.size() != m_scalarIndexes.size())
+    m_scalarIndexes.clear();
+
   // If we don't have the scalar indexes, we sort the names and then save the
   // indexes, these will be used to preserve the displayed order even after
   // a rename.
   if (m_scalarIndexes.isEmpty()) {
-    auto scalars = dataSource->listScalars();
     auto sortedScalars = scalars;
 
     // sort the scalars names