Property.expressionError only compiled the expression, so one that compiles
but throws or yields a non-finite number read as "" while expr.errors
reported it. It now evaluates the property's expression at the comp's
current time through the same per-property check expr.errors uses
(expr_tools::property_error), without rendering anything. Without an
evaluator, an enabled expression falls back to the syntax check.
Fixes#3219
vangel76
cdbb884f28