The condition "context_start < context_end" is strictly weaker
than "context_end - context_start >= 50", so we don't need both.
Oversight in commit ffd3944a, noted by tanghy.fnst.

In passing, line-wrap a nearby test to make it more readable.

Discussion: https://postgr.es/m/OS0PR01MB61137C4054774F44E3A9DC89FBC69@OS0PR01MB6113.jpnprd01.prod.outlook.com