sys: FspFsvolQueryDirectoryCopy: add missing continue

A single line change in FspFsvolQueryDirectoryCopy fixes GitHub issue #475.
This commit also includes a test for detecting duplicate directory entries.
Credit for the investigation and reproduction of this issue goes to GitHub
user @hach-que.

tst/memfs/memfs.h

@@ -38,6 +38,7 @@ enum
     MemfsCaseInsensitive                = 0x80000000,
     MemfsFlushAndPurgeOnCleanup         = 0x40000000,
     MemfsLegacyUnlinkRename             = 0x20000000,
+    MemfsNoSlowio                       = 0x10000000,
 };
 
 #define MemfsCreate(Flags, FileInfoTimeout, MaxFileNodes, MaxFileSize, VolumePrefix, RootSddl, PMemfs)\