Fix filters being called multiple times, consistent intialization for…

[jsteinberg]

… method_not_found errors

I also think this is a more consistent fix to this: #1446

[jsteinberg]

This resolves #1426 / #1424

[namusyaka]

Could you get rid of the duplication of env[Grape::Env::GRAPE_METHOD_NOT_ALLOWED] ?

[jsteinberg]

Sure. It only is duplicated if it is present so I thought it was okay. Do you have a preference between these two?

1:

if (allowed_methods = env[Grape::Env::GRAPE_METHOD_NOT_ALLOWED])
  raise Grape::Exceptions::MethodNotAllowed, header.merge('Allow' => allowed_methods)
end

2:

allowed_methods = env[Grape::Env::GRAPE_METHOD_NOT_ALLOWED]
raise Grape::Exceptions::MethodNotAllowed, header.merge('Allow' => allowed_methods) if allowed_methods

[namusyaka]

Maybe 1 will be aborted by rubocop, so I'd like to vote to 2 approach.
Btw, there are two reasons why I have pointed out.

1. By assiging variable, we can reduce number of characters of the line.
2. The assigned variable can be used in three places.

[jsteinberg]

rubocop was fine with both(the parens around it quieted it). But it caused the class to have too many lines. option 2 seems to take care of that restraint, but either that limit will need to be raised soon or....

and the 3rd instance of env[Grape::Env::GRAPE_METHOD_NOT_ALLOWED] is actually completely redundant since we are raising an exception. So I removed it with my latest change.

[namusyaka]

@jsteinberg Awesome. Your patch seems to work well.
Thank you so much!

[dblock]

Excellent, merging.