Up to 50 oil tankers are waiting to unload cargo in the port of Rotterdam, the highest number since 2009 and another sign that, amid a glut, crude is struggling to find a home. The unusually high number of ships idling outside of Europe’s busiest port comes as onshore tanks around the world brim with crude and products like fuel or jet oil. That has sent buyers and sellers scrambling to find storage, using tankers and even…