C++: Add sanity check to Instruction.qll

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Instruction.qll

@@ -268,6 +268,16 @@ module InstructionSanity {
   }
 }
 
+query predicate switchInstructionWithoutDefaultEdge(
+  SwitchInstruction switchInstr, string message, IRFunction func, string funcText
+) {
+  not exists(switchInstr.getDefaultSuccessor()) and
+  message =
+    "SwitchInstruction " + switchInstr.toString() + " without a DefaultEdge in function '$@'." and
+  func = switchInstr.getEnclosingIRFunction() and
+  funcText = Language::getIdentityString(func.getFunction())
+}
+
 /**
  * Gets an `Instruction` that is contained in `IRFunction`, and has a location with the specified
  * `File` and line number. Used for assigning register names when printing IR.