Edit the precedence constraint and set the Evaluation operation setting to 'Expression'. Then use the Expression text box to check your variable value as such: @[User::CheckData] > 0.

You'll notice that the expression builder is not available here for whatever reason so you'll have to manually enter the expression. If you run into syntax errors, pull up an expression builder in another task and use it to build the expression, then cut/paste to the Precedence constraint.