set reminder to AT_START if its custom with 0 minutes

app/src/main/java/com/simplemobiletools/calendar/Config.java

@@ -62,6 +62,9 @@ public class Config {
     }
 
     public void setDefaultReminderType(int type) {
+        if (type == Constants.REMINDER_CUSTOM && getDefaultReminderMinutes() == 0)
+            type = Constants.REMINDER_AT_START;
+
         mPrefs.edit().putInt(Constants.REMINDER_TYPE, type).apply();
     }
 

app/src/main/kotlin/com/simplemobiletools/calendar/activities/SettingsActivity.kt

@@ -87,7 +87,9 @@ class SettingsActivity : SimpleActivity() {
             2 -> Constants.DAY_MINS
             else -> 1
         }
+
         mConfig.defaultReminderMinutes = Integer.valueOf(value) * multiplier
+        mConfig.defaultReminderType = Constants.REMINDER_CUSTOM
         toast(R.string.reminder_saved)
         hideKeyboard()
     }