Statistics: Minor style-nit followup to #10968

Too late to avoid the whitespace diff churn, unfortunately ;).

plugins/statistics.koplugin/main.lua

@@ -3056,7 +3056,7 @@ function ReaderStatistics:onShowReaderProgress()
 end
 
 function ReaderStatistics:onShowBookStats()
-    if self:isEnabled() then
+    if not self:isEnabled() then return end
     self.kv = KeyValuePage:new{
         title = _("Current statistics"),
         kv_pairs = self:getCurrentStat(),
@@ -3065,7 +3065,6 @@ function ReaderStatistics:onShowBookStats()
     }
     UIManager:show(self.kv)
 end
-end
 
 function ReaderStatistics:getCurrentBookReadPages()
     if not self:isEnabled() then return end