DeskTop: Don't show error checking all drives with empty floppy

When polling Disk II devices, ERR_DEVICE_NOT_CONNECTED is returned by
the ProDOS driver if there is no disk in the drive. This case wasn't
explicitly handled by Special > Check All Drives (or Special > Check
Drive) so an error was shown. Filter that out.

Doesn't repro in Virtual ][ but does repro in MAME and this looks like
a real issue, not emulator.

Probably regressed with the rework after the 1.5 branch.

Author: inexorabletash

src/desktop/main.s

@@ -4873,6 +4873,15 @@ close_loop:
         jmp     FormatUnitNum
     END_IF
 
+    IF A = #ERR_DEVICE_NOT_CONNECTED
+        ;; If Disk II this just means it is empty
+        ldy     devlst_index
+        lda     DEVLST,y
+        ;; NOTE: Not masked with `UNIT_NUM_MASK`, `IsDiskII` handles it.
+        jsr     IsDiskII
+        RTS_IF ZS               ; is Disk II; that's fine
+    END_IF
+
         ;; Show an alert for other errors only if requested by the
         ;; caller. The history here is that an error should only be
         ;; shown if there is an unexpected type of error (i.e. not one

tests/check_all_drives.lua

@@ -0,0 +1,14 @@
+--[[ BEGINCONFIG ========================================
+
+DISKARGS="-hard1 $HARDIMG"
+
+======================================== ENDCONFIG ]]--
+-- NOTE: Need at least one empty Disk II drive
+
+test.Step(
+  "No error if floppy is empty",
+  function()
+    a2d.InvokeMenuItem(a2d.SPECIAL_MENU, a2d.SPECIAL_CHECK_ALL_DRIVES)
+    a2d.WaitForRepaint()
+    test.Snap("verify no alert shown")
+end)