Only show Subtotal Prefix with Transactions

If `Show subtotals only (hide transactional data)` is selected then the `Total For` prefix should not be shown.

gnucash/report/trep-engine.scm

@@ -1762,7 +1762,10 @@ be excluded from periodic reporting.")
               (data-columns (car list-of-commodities))))
             (loop "" (cdr list-of-commodities))))))
 
-    (define (total-string str) (string-append (G_ "Total For ") str))
+    (define (total-string str)
+      (if (opt-val pagename-sorting optname-show-subtotals-only)
+        str
+        (string-append (G_ "Total For ") str)))
 
     ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
     ;; renderers