ui: set app list button text on main thread

Hopefully will fix, "Only the original thread that creted a view
hierarchy can touch its views."

Reported-by: Damir <2k1dmg@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

ui/src/main/java/com/wireguard/android/fragment/AppListDialogFragment.kt

@@ -63,8 +63,8 @@ class AppListDialogFragment : DialogFragment() {
                 withContext(Dispatchers.Main.immediate) {
                     appData.clear()
                     appData.addAll(applicationData)
+                    setButtonText()
                 }
-                setButtonText()
             } catch (e: Throwable) {
                 withContext(Dispatchers.Main.immediate) {
                     val error = ErrorMessages[e]