inetcomm: Fix memory leak.

Found by Valgrind.

dlls/inetcomm/mimeole.c

@@ -1610,6 +1610,7 @@ static HRESULT create_body_offset_list(IStream *stm, const char *boundary, struc
     } while(1);
 
 end:
+    HeapFree(GetProcessHeap(), 0, nl_boundary);
     HeapFree(GetProcessHeap(), 0, buf);
     return hr;
 }