Implement getLong for ContentValuesCursor.

This is required because SQLite "rowids" are 64 bit integers:

> all rows within SQLite tables have a 64-bit signed integer
> key that uniquely identifies the row within its table."

https://sqlite.org/lang_createtable.html#rowid

app/src/main/java/org/fdroid/fdroid/data/ContentValuesCursor.java

@@ -65,7 +65,10 @@ class ContentValuesCursor extends AbstractCursor {
 
     @Override
     public long getLong(int i) {
-        throw new IllegalArgumentException("unimplemented");
+        if (values[i] instanceof Long) {
+            return (Long) values[i];
+        }
+        throw new IllegalArgumentException("Value is not a Long");
     }
 
     @Override