show: stringify filtered list of tags before testing emptiness

`names % "{ifeq(name, 'tip', '', name)}"}"` may return [''], which shouldn't
be falsy, but it is thanks to a templater bug. This patch converts [''] to ''
before testing truthness.

mercurial/templates/map-cmdline.show

@@ -15,7 +15,8 b" cset_shortnode = '{labelcset(shortest(no"
 # Treat branch and tags specially so we don't display "default" or "tip"
 cset_namespace = '{ifeq(namespace, "branches", names_branches, ifeq(namespace, "tags", names_tags, names_others))}'
 names_branches = '{ifeq(branch, "default", "", " ({label('log.{colorname}', branch)})")}'
-names_tags = '{if(names % "{ifeq(name, 'tip', '', name)}", " ({label('log.{colorname}', join(names % "{ifeq(name, 'tip', '', name)}", ' '))})")}'
+names_tags = '{if(stringify(names % "{ifeq(name, 'tip', '', name)}"),
+                  " ({label('log.{colorname}', join(names % "{ifeq(name, 'tip', '', name)}", ' '))})")}'
 names_others = '{if(names, " ({label('log.{colorname}', join(names, ' '))})")}'
 
 cset_shortdesc = '{label("log.description", desc|firstline)}'