Fixup Add invariant on component index being in range

Author: thomasspriggs

src/util/std_expr.h

@@ -1827,13 +1827,19 @@ class struct_exprt:public exprt
   /// \return The expression for a named component of this struct.
   exprt &component(const irep_idt &name)
   {
-    return operands()[to_struct_type(type()).component_number(name)];
+    const auto index = to_struct_type(type()).component_number(name);
+    DATA_INVARIANT(
+      index < operands().size(), "component matching index should exist");
+    return operands()[index];
   }
 
   /// \return The expression for a named component of this struct.
   const exprt &component(const irep_idt &name) const
   {
-    return operands()[to_struct_type(type()).component_number(name)];
+    const auto index = to_struct_type(type()).component_number(name);
+    DATA_INVARIANT(
+      index < operands().size(), "component matching index should exist");
+    return operands()[index];
   }
 };