UnaryOpPattern et al. cause loop in PatternProxy (Pdefn) for single values.

[telephon]

This is related to #2411, but can be fixed independently, for now.

When used with an operator, PatternProxy doesn't embed in Pattern correctly. It loops single values, while it shouldn't.

// a doesn't loop (is correct)
a = PatternProxy(7);
b = Pseq([1, 2, 3, a, 5], inf);
b.asStream.nextN(8);

// a loops (wrong)
a = PatternProxy(7).neg; // call an operator, result is a UnaryOpStream
b = Pseq([1, 2, 3, a, 5], inf);
b.asStream.nextN(8);