Sync addRangeTableEntryForENR() with its peer functions.

addRangeTableEntryForENR had a check for pstate != NULL, which Coverity
pointed out was rather useless since it'd already dereferenced pstate
before that.  More to the point, we'd established policy in commit
bc93ac12 that we'd require non-NULL pstate for all addRangeTableEntryFor*
functions; this test was evidently copied-and-pasted from some older
version of one of those functions.  Make it look more like the others.

In passing, make an elog message look more like the rest of the code,
too.

Michael Paquier