Fix not all %transfiletriggerpostun triggers executing (RhBug:1514085)

Trigger indexes need to be reset to zero when the package changes,
otherwise only the first %transfiletriggerpostun encountered will
get stored and run.

This bug has been there since introduction of file triggers so 4.13.x
and 4.14.x are affected and will need updates. Besides triggeres just
not executing, I suppose this might in some circumstances cause wrong
triggers executing.
Trigger indexes must be reset to zero when package changes.

lib/rpmtriggers.c

@@ -106,7 +106,6 @@ void rpmtriggersPrepPostUnTransFileTrigs(rpmts ts, rpmte te)
     rpmfiles files;
     rpmds rpmdsTriggers;
     rpmds rpmdsTrigger;
-    int tix = 0;
 
     ii = rpmdbIndexIteratorInit(rpmtsGetRdb(ts), RPMDBI_TRANSFILETRIGGERNAME);
     mi = rpmdbNewIterator(rpmtsGetRdb(ts), RPMDBI_PACKAGES);
@@ -131,6 +130,7 @@ void rpmtriggersPrepPostUnTransFileTrigs(rpmts ts, rpmte te)
     if (rpmdbGetIteratorCount(mi)) {
 	/* Filter triggers and save only trans postun triggers into ts */
 	while ((trigH = rpmdbNextIterator(mi)) != NULL) {
+	    int tix = 0;
 	    rpmdsTriggers = rpmdsNew(trigH, RPMTAG_TRANSFILETRIGGERNAME, 0);
 	    while ((rpmdsTrigger = rpmdsFilterTi(rpmdsTriggers, tix))) {
 		if ((rpmdsNext(rpmdsTrigger) >= 0) &&