Fixed current tiddler overwrite in tabs macro

Fixed a side-effect of 03519c14b0 from
@matabele whereby the current tiddler is overwritten by the
`<$tiddler>` widget, which means that it is not accessible when
rendering the caption of the tab.

This causes a problem with eg the “Add Plugins” modal where it breaks
the count on the tabs.

core/wiki/macros/tabs.tid

@@ -4,14 +4,16 @@ tags: $:/tags/Macro
 \define tabs(tabsList,default,state:"$:/state/tab",class,template)
 <div class="tc-tab-set $class$">
 <div class="tc-tab-buttons $class$">
-<$list filter="$tabsList$ +[nsort[order]]" variable="currentTab"><$tiddler tiddler=<<currentTab>> ><$button set=<<qualify "$state$">> setTo=<<currentTab>> default="$default$" selectedClass="tc-tab-selected" tooltip={{!!tooltip}}>
+<$list filter="$tabsList$ +[nsort[order]]" variable="currentTab"><$set name="save-currentTiddler" value=<<currentTiddler>>><$tiddler tiddler=<<currentTab>>><$button set=<<qualify "$state$">> setTo=<<currentTab>> default="$default$" selectedClass="tc-tab-selected" tooltip={{!!tooltip}}>
+<$tiddler tiddler=<<save-currentTiddler>>>
 <$set name="tv-wikilinks" value="no">
 <$transclude tiddler=<<currentTab>> field="caption">
 <$macrocall $name="currentTab" $type="text/plain" $output="text/plain"/>
 </$transclude>
-</$set>
-</$button></$tiddler></$list>
-</div><div class="tc-tab-divider $class$"/><div class="tc-tab-content $class$">
+</$set></$tiddler></$button></$tiddler></$set></$list>
+</div>
+<div class="tc-tab-divider $class$"/>
+<div class="tc-tab-content $class$">
 <$list filter="$tabsList$" variable="currentTab">
 
 <$reveal type="match" state=<<qualify "$state$">> text=<<currentTab>> default="$default$">