Implement fallback procedures for Inno Download Plugin

Added no-op fallback procedures for Inno Download Plugin.

win32/installer/zoitechat.iss.tt

@@ -5,7 +5,10 @@
 ;#define PROJECTDIR "C:\...\zoitechat\win32\installer\"
 
 ;http://mitrich.net23.net/?/inno-download-plugin.html
+#ifexist "idp.iss"
+#define USE_INNO_DOWNLOAD_PLUGIN
 #include <idp.iss>
+#endif
 
 [Setup]
 AppName=ZoiteChat
@@ -203,6 +206,22 @@ Name: "{commonappdata}\Microsoft\Internet Explorer\Quick Launch\ZoiteChat"; File
 BeveledLabel= {#APPNAM}
 
 [Code]
+#ifndef USE_INNO_DOWNLOAD_PLUGIN
+// The Inno Download Plugin isn't always installed in CI environments.
+// Provide no-op fallback procedures so installer compilation still succeeds.
+procedure idpDownloadAfter(PageID: Integer);
+begin
+end;
+
+procedure idpClearFiles;
+begin
+end;
+
+procedure idpAddFile(URL: String; Filename: String);
+begin
+end;
+#endif
+
 /////////////////////////////////////////////////////////////////////
 procedure InitializeWizard;
 begin