The current `loadClass()` implementation tries to load a class from the first matching prefix then stops, producing false-negative results. This is especially evident in groups of related libraries, such as Doctrine:
Each of these libraries is submoduled into a different vendor directory. Depending on what order these libraries are added to a UniversalClassLoader instance, classes may or may not actually be loaded. This fix continues searching registered namespaces and prefixes if the first partial match is negative.