inline doc fails for non existing language documentation

Inline documentation should fall back to en_US documentation when Scilab is using an "unsupported" language.

--> setlanguage en_PH

 ans = 

  T

--> getHelpPage cos
at line     7 of function getPage     ( C:\Program Files\scilab-2025.1.0\modules\helptools\macros\getHelpPage.sci line 31 )
at line     7 of function getHelpPage ( C:\Program Files\scilab-2025.1.0\modules\helptools\macros\getHelpPage.sci line 7 )

Invalid index.

--> setlanguage en_US

 ans = 

  T

--> getHelpPage cos

 ans = [struct] with fields:

  refname: [struct] with fields:
      type = "refname"
      children: [struct] with fields:
          type = "text"
          children = []
          string = "cos"
      string = []
  refpurpose: [struct] with fields:
      type = "refpurpose"
      children: [struct] with fields:
          type = "text"
          children = []
          string = "cosine function"
      string = []
  synopsis: [struct] with fields:
      type = "synopsis"
      children = []
      string = "[y]=cos(x)"
  varlist: [struct] with fields:
      type = "variablelist"
      children: [struct] with fields:
          type = "varlistentry"
          children: [1x2 struct]
          string = []
      string = []
  seealso = ["cosd","acos","acosd","cosm"]