Fix settings page crashing

Select.tsx was crashing if it couldn't
find a label for the selected value.

Select.tsx

@@ -41,7 +41,7 @@ export default function Select({
         <Button
           onPress={() => setShow(true)}
           style={{alignSelf: 'flex-start', marginTop: MARGIN}}>
-          {selected.label}
+          {selected?.label}
         </Button>
       }>
       {items.map(item => (

SettingsPage.tsx

@@ -224,7 +224,7 @@ export default function SettingsPage() {
           />
           {'theme'.includes(term.toLowerCase()) && (
             <Select
-              value={theme}
+              value={theme || 'system'}
               onChange={changeTheme}
               items={[
                 {label: 'Follow system theme', value: 'system'},

use-theme.ts

@@ -6,7 +6,7 @@ export const ThemeContext = createContext<{
   setTheme: (value: string) => void
   setColor: (value: string) => void
 }>({
-  theme: '',
+  theme: 'system',
   color: '',
   setTheme: () => null,
   setColor: () => null,