Fix property extraction from Lua for IntProperty

include/openspace/properties/scalar/intproperty.h

@@ -44,6 +44,9 @@ public:
     int typeLua() const override;
 
     using TemplateProperty<int>::operator=;
+
+private:
+    int fromLuaConversion(lua_State* state) const override;
 };
 
 } // namespace openspace::properties

src/properties/scalar/intproperty.cpp

@@ -41,4 +41,16 @@ int IntProperty::typeLua() const {
     return LUA_TNUMBER;
 }
 
+int IntProperty::fromLuaConversion(lua_State* state) const {
+    if (ghoul::lua::hasValue<double>(state)) {
+        return static_cast<int>(ghoul::lua::value<double>(state));
+    }
+    else if (ghoul::lua::hasValue<int>(state)) {
+        return ghoul::lua::value<int>(state);
+    }
+    else {
+        throw ghoul::RuntimeError(fmt::format("Error extracting value in IntProperty"));
+    }
+}
+
 } // namespace openspace::properties