fix error calling clearThingsToTranslate when it is null in own plans

client/src/components/Plans/Plans.jsx

@@ -138,7 +138,7 @@ const Plans = (props) => {
         }
         setTimeout(() => {event.target.scrollIntoView({ behavior: "smooth", block: "center" });}, 300);
       } else { // close history
-        clearThingsToTranslate();
+        if(clearThingsToTranslate) clearThingsToTranslate();
         setTimeout(() => {event.target.scrollIntoView({ behavior: "smooth", block: "end" });}, 300);
       }
       return !prevState;