xargs: Fix boring memory leak

It's only 1K (BUFSIZ), and it's immediately before xargs finishes anyway.
However, I ran into it and know how to fix it, so let's clean this up.

Userland/Utilities/xargs.cpp

@@ -198,6 +198,7 @@ bool read_items(FILE* fp, char entry_separator, Function<Decision(StringView)> c
                 perror("getdelim");
                 fail = true;
             }
+            free(item);
             break;
         }