irfanview: add "if exist" check before running rmdir on removal

I was getting:

Exit code returned non-successful value: 2
Package: Irfanview.
Command:
cmd /c rmdir /s /q "%programfiles(x86)%\irfanview"
Removal of Irfanview successful.

i.e. the rmdir was returning 2 ("directory not found") but because that
was the final remove cmd and the package check condition was no longer
satisfied, wpkg was happy that the removal had completed.

packages/irfanview.xml

@@ -26,7 +26,7 @@
     <remove cmd='"%programfiles(x86)%\irfanview\iv_uninstall.exe" /silent' />
     <remove cmd='cmd /c %WPKGSOFTWARE%\wpkg\tools\waitforprocess.cmd iv_uninstall.exe' />
     <!-- the uninstaller leaves itself behind, so remove it -->
-    <remove cmd='cmd /c rmdir /s /q "%programfiles(x86)%\irfanview"' />
+    <remove cmd='cmd /c if exist "%programfiles(x86)%irfanview" rmdir /s /q "%programfiles(x86)%\irfanview"' />
   </package>
 
 </packages:packages>