Added condition in graphql.install for non empty variable

[aarohiprasad]

Context:

1. Install Drupal in (standard install profile)
2. Install graphQL module
3. Uninstall GraphQL module and see error

 ---- -------------- -------- ---------- -------------------------------------- 
  ID   Date           Type     Severity   Message                               
 ---- -------------- -------- ---------- -------------------------------------- 
  46   04/Jul 15:32   php      Error      TypeError: array_keys(): Argument #1  
                                          ($array) must be of type array, null  
                                          given in array_keys() (line 40 of     
                                          /var/www/html/web/modules/contrib/gr  
                                          aphql/graphql.install).   

This PR adds an 'if' condition in graphql.install to check if language module is correctly enabled

[Kingdutch]

Thanks for reporting this bug, I think we can make a more focused change though that more clearly communicates what is going wrong :D

[darvanen]

I also ran into this issue.