Fix issue with iterative removal

In testing zend-eventmanager, I discovered a race condition with the
following:

```php
while ($queue->contains($listener)) {
    $queue->remove($listener);
}
```

In debugging, I determined that while `remove()` was correctly
identifying that it had the datum, it was not using the correct index in
the value array to unset it, which would leave it in place. Modifying
the code to use `key()` on the values array allows it to work as
expected.

Author: weierophinney

src/FastPriorityQueue.php

@@ -135,7 +135,8 @@ public function remove($datum)
         $this->rewind();
         while ($this->valid()) {
             if (current($this->values[$this->maxPriority]) === $datum) {
-                unset($this->values[$this->maxPriority][$this->subIndex]);
+                $index = key($this->values[$this->maxPriority]);
+                unset($this->values[$this->maxPriority][$index]);
                 --$this->count;
                 return true;
             }

test/FastPriorityQueueTest.php

@@ -238,4 +238,51 @@ public function testRewindShouldNotRaiseErrorWhenQueueIsEmpty()
         $queue->rewind();
         restore_error_handler();
     }
+
+    public function testRemoveShouldFindItemEvenIfMultipleItemsAreInQueue()
+    {
+        $prototype = function ($e) {
+        };
+
+        $queue = new FastPriorityQueue();
+        $this->assertTrue($queue->isEmpty());
+
+        $listeners = [];
+        for ($i = 0; $i < 5; $i += 1) {
+            $listeners[] = $listener = clone $prototype;
+            $queue->insert($listener, 1);
+        }
+
+        $remove   = array_rand(array_keys($listeners));
+        $listener = $listeners[$remove];
+
+        $this->assertTrue($queue->contains($listener));
+        $this->assertTrue($queue->remove($listener));
+        $this->assertFalse($queue->contains($listener));
+    }
+
+    public function testIterativelyRemovingItemsShouldRemoveAllItems()
+    {
+        $prototype = function ($e) {
+        };
+
+        $queue = new FastPriorityQueue();
+        $this->assertTrue($queue->isEmpty());
+
+        $listeners = [];
+        for ($i = 0; $i < 5; $i += 1) {
+            $listeners[] = $listener = clone $prototype;
+            $queue->insert($listener, 1);
+        }
+
+        for ($i = 0; $i < 5; $i += 1) {
+            $listener = $listeners[$i];
+            $queue->remove($listener);
+        }
+
+        for ($i = 0; $i < 5; $i += 1) {
+            $listener = $listeners[$i];
+            $this->assertFalse($queue->contains($listener), sprintf('Listener %s remained in queue', $i));
+        }
+    }
 }