Fix PSR warnings for optimized autoloader, refs #8397, refs #8403

src/Composer/Autoload/ClassMapGenerator.php

@@ -111,7 +111,7 @@ class ClassMapGenerator
             foreach ($classes as $class) {
                 // skip classes not within the given namespace prefix
                 // TODO enable in Composer v1.11 or 2.0 whichever comes first
-                if (/* null === $autoloadType && */ null !== $namespace && 0 !== strpos($class, $namespace)) {
+                if (/* null === $autoloadType && */ null !== $namespace && '' !== $namespace && 0 !== strpos($class, $namespace)) {
                     continue;
                 }