revlogdeltas: move special cases around raw revisions in finddeltainfo

The method already contains logic for no-diff cases. Having everything in the
same place is more consistent and unlocks other code improvements.

mercurial/revlog.py

@@ -1965,13 +1965,7 b' class revlog(object):'
 
         revinfo = _revisioninfo(node, p1, p2, btext, textlen, cachedelta, flags)
 
-        # no delta for flag processor revision (see "candelta" for why)
-        # not calling candelta since only one revision needs test, also to
-        # avoid overhead fetching flags again.
-        if flags & REVIDX_RAWTEXT_CHANGING_FLAGS:
-            deltainfo = None
-        else:
-            deltainfo = deltacomputer.finddeltainfo(revinfo, fh)
+        deltainfo = deltacomputer.finddeltainfo(revinfo, fh)
 
         if deltainfo is not None:
             base = deltainfo.base

mercurial/revlogutils/deltas.py

@@ -703,6 +703,12 b' class deltacomputer(object):'
         if not revinfo.textlen:
             return None # empty file do not need delta
 
+        # no delta for flag processor revision (see "candelta" for why)
+        # not calling candelta since only one revision needs test, also to
+        # avoid overhead fetching flags again.
+        if revinfo.flags & REVIDX_RAWTEXT_CHANGING_FLAGS:
+            return None
+
         cachedelta = revinfo.cachedelta
         p1 = revinfo.p1
         p2 = revinfo.p2