Fix internalASTError with decltype (regression, refs #11378)

[chrchr-github]

No description provided.

[chrchr-github]

= 'container(std :: string|wstring|u16string|u32string)'
|-x 'container(std :: string|wstring|u16string|u32string)'
`-{ 'container(std :: string|wstring|u16string|u32string)'
  |-::
  | |-std
  | `-string
  `-:: 'const signed char * const'
    |-( 'S::T'
    | |-decltype
    | `-. 'S::T'
    | | |-s 'S'
    | | `-t 'S::T'
    `-a

(
|-if
`-> 'bool'
  |-0 'signed int'
  `-:: 'const signed int'
    |-( 'S::T'
    | |-decltype
    | `-. 'S::T'
    | | |-s 'S'
    | | `-t 'S::T'
    `-X