[Popover] Fix the warning when anchorReference="anchorPosition" (#15182)
[Popover] Fix the warning when anchorReference="anchorPosition" (#15182)

* [Popover] fix for warning when passing undefined to anchorEl

* Update Popover.js

* do not check anchorEl if anchorReference is not set to anchorEl

* use suggested fix instead

mui-org/material-ui,allanalexandre/material-ui,callemall/material-ui,callemall/material-ui,callemall/material-ui,kybarg/material-ui,mui-org/material-ui,oliviertassinari/material-ui,oliviertassinari/material-ui,rscnt/material-ui,callemall/material-ui,rscnt/material-ui,mui-org/material-ui,mbrookes/material-ui,lgollut/material-ui,kybarg/material-ui,oliviertassinari/material-ui,rscnt/material-ui,mbrookes/material-ui,mbrookes/material-ui,kybarg/material-ui,kybarg/material-ui