Added protection against overflows in the wait time calculation.

Author: Prizephitah

src/Backoff.php

@@ -329,6 +329,7 @@ public function getWaitTime($attempt)
      */
     protected function cap($waitTime)
     {
+        $waitTime = $waitTime < 0 ? PHP_INT_MAX : $waitTime;
         return is_int($this->getWaitCap())
             ? min($this->getWaitCap(), $waitTime)
             : $waitTime;

tests/BackoffTest.php

@@ -151,6 +151,13 @@ public function testWaitCap()
         $this->assertEquals(5000, $b->getWaitTime(2));
     }
 
+    public function testWaitCapOverflow()
+    {
+        $b = new Backoff(1, new LinearStrategy(-1), 1000);
+
+        $this->assertEquals(1000, $b->getWaitTime(1));
+    }
+
     public function testWait()
     {
         $b = new Backoff(1, new LinearStrategy(50));