Check if imageflip is available
Check if imageflip is available

* imageflip() isn't available in PHP < 5.5
* fixes #14130

Ardinis/server,andreas-p/nextcloud-server,IljaN/core,IljaN/core,michaelletzgus/nextcloud-server,pmattern/server,IljaN/core,xx621998xx/server,whitekiba/server,pixelipo/server,pollopolea/core,whitekiba/server,lrytz/core,andreas-p/nextcloud-server,IljaN/core,sharidas/core,jbicha/server,endsguy/server,bluelml/core,endsguy/server,michaelletzgus/nextcloud-server,cernbox/core,whitekiba/server,Ardinis/server,endsguy/server,IljaN/core,jbicha/server,michaelletzgus/nextcloud-server,jbicha/server,owncloud/core,pollopolea/core,endsguy/server,cernbox/core,phil-davis/core,andreas-p/nextcloud-server,pollopolea/core,nextcloud/server,nextcloud/server,cernbox/core,bluelml/core,sharidas/core,lrytz/core,owncloud/core,pixelipo/server,jbicha/server,bluelml/core,pmattern/server,pixelipo/server,pollopolea/core,pollopolea/core,endsguy/server,cernbox/core,lrytz/core,lrytz/core,bluelml/core,owncloud/core,pmattern/server,nextcloud/server,pixelipo/server,jbicha/server,Ardinis/server,xx621998xx/server,sharidas/core,andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,owncloud/core,xx621998xx/server,whitekiba/server,Ardinis/server,sharidas/core,sharidas/core,xx621998xx/server,lrytz/core,xx621998xx/server,pixelipo/server,pmattern/server,michaelletzgus/nextcloud-server,cernbox/core,Ardinis/server,bluelml/core,pmattern/server,owncloud/core,whitekiba/server