From Tom, return 0xFF on invalid drives for int 21h/1c get drive allocation information (sectors/clusters)

git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/trunk@1376 6ac86273-5f31-0410-b378-82cca8765d1b

kernel/inthndlr.c

@@ -651,10 +651,14 @@ dispatch:
       {
         BYTE FAR *p;
 
-        p = FatGetDrvData(lr.DL, &lr.AL, &lr.CX, &lr.DX);
+        if ((p = FatGetDrvData(lr.DL, &lr.AL, &lr.CX, &lr.DX)) != NULL)
+        {
           lr.DS = FP_SEG(p);
           lr.BX = FP_OFF(p);
         }
+        else
+          lr.AL = 0xff;  /* return 0xff on invalid drive */
+      }
       break;
 
       /* Get default DPB                                              */