Fix memory corruption with NSMutableData(length:)

Author: mbvreddy

Foundation/NSData.swift

@@ -907,7 +907,7 @@ extension NSMutableData {
 
     public convenience init?(length: Int) {
         let memory = malloc(length)
-        self.init(bytes: memory, length: length, copy: false) { buffer, amount in
+        self.init(bytes: memory, length: length, copy: true) { buffer, amount in
             free(buffer)
         }
     }