Protect needed_lazy_methods access in an if-block

If we are not using CI lazy methods here (as could happen after the
change from the previous commit that makes sure convert_single_method is
run for all methods), needed_lazy_methods is an empty optional and we
cannot access it.

Author: antlechner

jbmc/src/java_bytecode/java_bytecode_language.cpp

@@ -1312,24 +1312,27 @@ bool java_bytecode_languaget::convert_single_method(
     return false;
   }
 
-  // The return of an opaque function is a source of an otherwise invisible
-  // instantiation, so here we ensure we've loaded the appropriate classes.
-  const java_method_typet function_type = to_java_method_type(symbol.type);
-  if(
-    const pointer_typet *pointer_return_type =
-      type_try_dynamic_cast<pointer_typet>(function_type.return_type()))
+  if(needed_lazy_methods)
   {
-    // If the return type is abstract, we won't forcibly instantiate it here
-    // otherwise this can cause abstract methods to be explictly called
-    // TODO(tkiley): Arguably no abstract class should ever be added to
-    // TODO(tkiley): ci_lazy_methods_neededt, but this needs further
-    // TODO(tkiley): investigation
-    namespacet ns{symbol_table};
-    const java_class_typet &underlying_type =
-      to_java_class_type(ns.follow(pointer_return_type->subtype()));
-
-    if(!underlying_type.is_abstract())
-      needed_lazy_methods->add_all_needed_classes(*pointer_return_type);
+    // The return of an opaque function is a source of an otherwise invisible
+    // instantiation, so here we ensure we've loaded the appropriate classes.
+    const java_method_typet function_type = to_java_method_type(symbol.type);
+    if(
+      const pointer_typet *pointer_return_type =
+        type_try_dynamic_cast<pointer_typet>(function_type.return_type()))
+    {
+      // If the return type is abstract, we won't forcibly instantiate it here
+      // otherwise this can cause abstract methods to be explictly called
+      // TODO(tkiley): Arguably no abstract class should ever be added to
+      // TODO(tkiley): ci_lazy_methods_neededt, but this needs further
+      // TODO(tkiley): investigation
+      namespacet ns{symbol_table};
+      const java_class_typet &underlying_type =
+        to_java_class_type(ns.follow(pointer_return_type->subtype()));
+
+      if(!underlying_type.is_abstract())
+        needed_lazy_methods->add_all_needed_classes(*pointer_return_type);
+    }
   }
 
   INVARIANT(declaring_class(symbol), "Method must have a declaring class.");