Fix crash on anonymous splat in find pattern and {**nil}

[ahogappa]

Two pattern-matching forms crash during AST construction on master:

case ary
in [*, x, *rest]
  x
end
# => lib/typeprof/core/ast.rb:334:in 'create_pattern_node':
#    undefined method 'type' for nil (NoMethodError)

case h
in {**nil}
  1
end
# => lib/typeprof/core/ast/pattern.rb:42:in 'initialize':
#    undefined method 'value' for an instance of Prism::NoKeywordsParameterNode

Prism represents an anonymous splat as a SplatNode whose expression is nil, and HashPatternNode#rest can be a NoKeywordsParameterNode, which has no value. Both were passed to AST.create_pattern_node unchecked. ArrayPatternNode already guards against these, so this applies the same handling to FindPatternNode and HashPatternNode.

[sinsoku]

Thanks!