Fixed durability not working for first iteration of generator.

src/Porter.php

@@ -96,7 +96,12 @@ private function fetch(ProviderResource $resource, CacheAdvice $cacheAdvice, $fe
         if (($records = \ScriptFUSION\Retry\retry(
             $fetchAttempts,
             function () use ($provider, $resource) {
-                return $provider->fetch($resource);
+                if (($records = $provider->fetch($resource)) instanceof \Iterator) {
+                    // Force generator to run until first yield to provoke an exception.
+                    $records->valid();
+                }
+
+                return $records;
             },
             function (\Exception $exception) use ($fetchExceptionHandler) {
                 // Throw exception if unrecoverable.

test/Integration/Porter/PorterTest.php

@@ -300,6 +300,23 @@ public function testCustomFetchExceptionHandler()
         $this->porter->import($this->specification);
     }
 
+    /**
+     * Tests that when a generator throws a recoverable exception before the first yield, the fetch is retried.
+     *
+     * Note this does not support cases where exceptions may be thrown in subsequent iterations.
+     */
+    public function testGeneratorException()
+    {
+        $this->provider->shouldReceive('fetch')->once()->andReturnUsing(function () {
+            throw new RecoverableConnectorException;
+
+            yield;
+        });
+
+        $this->setExpectedException(FailingTooHardException::class, '1');
+        $this->porter->import($this->specification->setMaxFetchAttempts(1));
+    }
+
     #endregion
 
     public function testFilter()