Description:
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Recursive mkdir on ftp stream wrapper is incorrectly implemented. It issues a CWD and MKD without a required path parameter for the root folder.

Test script:
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<?php
mkdir("ftp://localhost:2121/one/two", 0755, true);

Expected result:
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Recursively create the directory structure.

Actual result:
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Fails becuase it creates invalid sequence of ftp commands:

2019/02/28 13:43:12 INFO  : f91b572012ab40453052: > CWD /one
2019/02/28 13:43:13 INFO  : f91b572012ab40453052: < 550 Directory change to /one failed: file does not exist
2019/02/28 13:43:13 INFO  : f91b572012ab40453052: > CWD
2019/02/28 13:43:13 INFO  : f91b572012ab40453052: < 553 action aborted, required param missing
2019/02/28 13:43:13 INFO  : f91b572012ab40453052: > MKD
2019/02/28 13:43:13 INFO  : f91b572012ab40453052: < 553 action aborted, required param missing