Introduce MonsterStruct.IsWalking()

Source/monster.cpp

@@ -5420,4 +5420,16 @@ void MonsterStruct::Petrify()
 	AnimInfo.IsPetrified = true;
 }
 
+bool MonsterStruct::IsWalking() const
+{
+	switch (_mmode) {
+	case MM_WALK:
+	case MM_WALK2:
+	case MM_WALK3:
+		return true;
+	default:
+		return false;
+	}
+}
+
 } // namespace devilution

Source/monster.h

@@ -201,6 +201,11 @@ struct MonsterStruct { // note: missing field _mAFNum
 	 * @brief Sets _mmode to MM_STONE
 	 */
 	void Petrify();
+
+	/**
+	 * @brief Is the monster currently walking?
+	 */
+	bool IsWalking() const;
 };
 
 extern int monstkills[MAXMONSTERS];