bash completion breaks on drush role:perm:add

[raffaelj]

Same issue as #5913. System and version are nearly the same.

When pressing Tab key to use bash completion with drush role:perm:add it hangs in a weird state with 2 newlines and waiting for input:

dummy@a14d6d62aff5:/var/www$ drush version
Drush version : 12.5.2.0 
dummy@a14d6d62aff5:/var/www$ drush role:perm:add 

^C
dummy@a14d6d62aff5:/var/www$

To Reproduce

• type drush role:perm:a, type Tab --> expands to drush role:perm:add as expected
• terminal shows drush role:perm:add (with the whitespace at the end), type Tab again --> broken state
• without the whitespace drush role:perm:add pressing Tab does nothing and nothing breaks