Only add column if it doesn't exist yet

Column can exist if there down- and upgrades

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/database/DBHelper.java

@@ -1,6 +1,7 @@
 package nodomain.freeyourgadget.gadgetbridge.database;
 
 import android.content.Context;
+import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
 
@@ -70,6 +71,13 @@ public class DBHelper {
         db.execSQL(statement);
     }
 
+    public static boolean existsColumn(String tableName, String columnName, SQLiteDatabase db) {
+        try (Cursor res = db.rawQuery("PRAGMA table_info('" + tableName + "')", null)) {
+            int result = res.getColumnIndex(columnName);
+            return result != -1;
+        }
+    }
+
     /**
      * WITHOUT ROWID is only available with sqlite 3.8.2, which is available
      * with Lollipop and later.

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/database/schema/ActivityDBUpdate_6.java

@@ -2,6 +2,7 @@ package nodomain.freeyourgadget.gadgetbridge.database.schema;
 
 import android.database.sqlite.SQLiteDatabase;
 
+import nodomain.freeyourgadget.gadgetbridge.database.DBHelper;
 import nodomain.freeyourgadget.gadgetbridge.database.DBUpdateScript;
 
 import static nodomain.freeyourgadget.gadgetbridge.database.DBConstants.KEY_CUSTOM_SHORT;
@@ -13,10 +14,12 @@ import static nodomain.freeyourgadget.gadgetbridge.database.DBConstants.TABLE_GB
 public class ActivityDBUpdate_6 implements DBUpdateScript {
     @Override
     public void upgradeSchema(SQLiteDatabase db) {
+        if (!DBHelper.existsColumn(TABLE_GBACTIVITYSAMPLES, KEY_CUSTOM_SHORT, db)) {
             String ADD_COLUMN_CUSTOM_SHORT = "ALTER TABLE " + TABLE_GBACTIVITYSAMPLES + " ADD COLUMN "
                     + KEY_CUSTOM_SHORT + " INT;";
             db.execSQL(ADD_COLUMN_CUSTOM_SHORT);
         }
+    }
 
     @Override
     public void downgradeSchema(SQLiteDatabase db) {