trydiff: call util.binary in only one place

It's practically free to call util.binary on empty or None content. By
relying on that, we can replace the current four call sites by one.

mercurial/patch.py

@@ -1796,7 +1796,6 b' def trydiff(repo, revs, ctx1, ctx2, modi'
                         else:
                             copyop = 'copy'
                         content1 = getfilectx(f1, ctx1).data()
-                binary = util.binary(content1) or util.binary(content2)
             elif f in removedset:
                 if opts.git:
                     # have we already reported a copy above?
@@ -1805,13 +1804,11 b' def trydiff(repo, revs, ctx1, ctx2, modi'
                         continue
                     else:
                         flag1 = ctx1.flags(f)
-                        binary = util.binary(content1)
-                else:
-                    binary = util.binary(content1)
             else:
                 flag1 = ctx1.flags(f)
                 flag2 = ctx2.flags(f)
-                binary = util.binary(content1) or util.binary(content2)
+
+            binary = util.binary(content1) or util.binary(content2)
 
         if losedatafn and not opts.git:
             if (binary or