Fix onClickAddonSettings not being optional

Author: GarboMuffin

src/components/menu-bar/menu-bar.jsx

@@ -552,7 +552,10 @@ class MenuBar extends React.Component {
                                 this.handleClickDesktopSettings
                             }
                             // eslint-disable-next-line react/jsx-no-bind
-                            onOpenCustomSettings={this.props.onClickAddonSettings.bind(null, 'editor-theme3')}
+                            onOpenCustomSettings={
+                                this.props.onClickAddonSettings &&
+                                this.props.onClickAddonSettings.bind(null, 'editor-theme3')
+                            }
                             onRequestClose={this.props.onRequestCloseSettings}
                             onRequestOpen={this.props.onClickSettings}
                             settingsMenuOpen={this.props.settingsMenuOpen}

src/components/menu-bar/tw-theme-blocks.jsx

@@ -120,7 +120,12 @@ const BlocksThemeMenu = ({
             />
         </div>
         <Submenu place={isRtl ? 'left' : 'right'}>
-            {[BLOCKS_THREE, BLOCKS_HIGH_CONTRAST, BLOCKS_DARK, BLOCKS_CUSTOM].map(i => (
+            {[
+                BLOCKS_THREE,
+                BLOCKS_HIGH_CONTRAST,
+                BLOCKS_DARK,
+                ...(onOpenCustomSettings ? [BLOCKS_CUSTOM] : [])
+            ].map(i => (
                 <ThemeMenuItem
                     key={i}
                     id={i}