Asm class generator should add set methods if there are only multi-arg.

Previous commit changed AsmBackedClassGenerator to only accept 1-arg methods
to be overridden. While this fixed the ClassFormatError, it also prevented
the generator from adding new 1-arg set methods, if there are only multi-arg
ones.

This commit updates the logic in AbstractClassGenerator to only attempt to
override if it is a 1-arg method. If not methods were overridden it will
add a new 1-arg method.