trydiff: make addindexmeta() unconditionally add index meta

The conditional-ness is not clear from the name and there is only one
caller, so it's clearer to check on the call site. Moving it also
makes addindexmeta() no longer close on the 'opts' variable.

mercurial/patch.py

@@ -1748,7 +1748,6 b' def trydiff(repo, revs, ctx1, ctx2, modi'
             header.append('new mode %s\n' % nmode)
 
     def addindexmeta(meta, oindex, nindex):
-        if opts.git:
             meta.append('index %s..%s\n' % (oindex, nindex))
 
     def gitindex(text):
@@ -1875,7 +1874,7 b' def trydiff(repo, revs, ctx1, ctx2, modi'
                 header.insert(0, diffline(join(a), join(b), revs))
             if dodiff == 'binary' and not opts.nobinary:
                 text = mdiff.b85diff(to, tn)
-                if text:
+                if text and opts.git:
                     addindexmeta(header, gitindex(to), gitindex(tn))
             else:
                 text = mdiff.unidiff(to, date1,