[FREELDR] fs.c: Fix path device name lookup

Suppose the list of devices contains, for example listed in this order:

  `multi(0)disk(0)rdisk(0)partition(1)`,
followed by:
  `multi(0)disk(0)rdisk(0)`,

then if someone attempts to open `multi(0)disk(0)rdisk(0)`, the code
would erroneously open `multi(0)disk(0)rdisk(0)partition(1)` instead.

Device name lookup now verifies that the device name being tested has
the same length as the one being opened.

Noticed by user "Xen", see:
https://reactos.org/forum/viewtopic.php?p=144840#p144840
> Wrong name comparison in ArcOpen (can open "device()partition()"
> instead of "device()" that was really requested)

Author: HBelusca

boot/freeldr/freeldr/lib/fs/fs.c

@@ -257,7 +257,7 @@ ARC_STATUS ArcOpen(CHAR* Path, OPENMODE OpenMode, ULONG* FileId)
          pEntry = pEntry->Flink)
     {
         pDevice = CONTAINING_RECORD(pEntry, DEVICE, ListEntry);
-        if (strncmp(pDevice->DeviceName, DeviceName, Length) == 0)
+        if ((strlen(pDevice->DeviceName) == Length) && (strncmp(pDevice->DeviceName, DeviceName, Length) == 0))
             break;
     }