OutOfMemoryException on unrecognised template

[Anthony Halliday]

Describe the bug

When attempting to compile a template that is unrecognised, the thread is blocked and eventually throws an OutOfMemoryException.

Expected behaviour:

The template parsing should either ignore the unsupported syntax or throw an "unsupported exception".

Test to reproduce

        [Fact]
        public void Compile_UnrecognisedExpression_ThrowsOutOfMemory()
        {
            var handlebars = Handlebars.Create();

            var source = "{{Text | example}}";

            Assert.Throws<OutOfMemoryException>(()=> handlebars.Compile(source));
        }

Other related info

My use-case for a templating library is to render HTML emails where templates are maintained by content editors. The above syntax is used by SendGrid to default values hence it's usage with Handlebars.Net.

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