fix #440, a hanging def no longer crashes the compiler

[ghost]

Fixes #440, where a hanging def or stream would crash the compiler. No test cases are included due to the complexity of testing for compiler errors and the imminent rework of the testing system.

class Foo
  def

will now give a parsing error:

"foo.enc" (line 4, column 1):
unexpected end of input
expecting identifier

instead of crashing the compiler.

[EliasC]

Looks good! Merging in a bit...