This caused output log to hang for several seconds rebuilding all lines of text.
Also fixes invariant string comparision on FTextSnapshot.
#jira UE-77849
#rb jamie.dale, alexander.sanoja
#ROBOMERGE-OWNER: ben.marsh
#ROBOMERGE-AUTHOR: rex.hill
#ROBOMERGE-SOURCE: CL 7651386 via CL 7654662 via CL 7654790
#ROBOMERGE-BOT: BUILD (Main -> Dev-Build) (v388-7785529)
[CL 7791643 by rex hill in Dev-Build branch]