commands: Read disableFastRender from flag even if it's not changed
commands: Read disableFastRender from flag even if it's not changed

Fixes #5353

mdhender/hugo,gohugoio/hugo,anthonyfok/hugo,fedelibre/hugo,anthonyfok/hugo,gohugoio/hugo,fedelibre/hugo,gohugoio/hugo,anthonyfok/hugo,fedelibre/hugo,mdhender/hugo,fedelibre/hugo,mdhender/hugo,mdhender/hugo