SWIFT-1051 Fix memory leak in BSONDocumentIterator

Author: kmahar

Sources/MongoSwift/BSON/BSONDocumentIterator.swift

@@ -36,7 +36,7 @@ public class BSONDocumentIterator: IteratorProtocol {
 
         let initialized = self.withMutableBSONIterPointer { iterPtr in
             self.document.withBSONPointer { docPtr in
-                bson_iter_init_find(iterPtr, docPtr, key.cString(using: .utf8))
+                bson_iter_init_find(iterPtr, docPtr, key)
             }
         }
 
@@ -56,7 +56,7 @@ public class BSONDocumentIterator: IteratorProtocol {
     /// Moves the iterator to the specified key. Returns false if the key does not exist. Returns true otherwise.
     internal func move(to key: String) -> Bool {
         self.withMutableBSONIterPointer { iterPtr in
-            bson_iter_find(iterPtr, key.cString(using: .utf8))
+            bson_iter_find(iterPtr, key)
         }
     }