installer: skip Experimental Options page, if empty

As of a75602a (installer: hide the "experimental" FSMonitor setting by
default, 2024-07-17), the FSMonitor option is hidden from the options
page unless the user had enabled it previously.

However, this then left the page blank (or: all options hidden), not a
good user experience. So let's skip it if it would appear blank.

This fixes git-for-windows/git#5231.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

installer/install.iss

@@ -423,6 +423,7 @@ const
     GP_BuiltinAddI     = 4;
     GP_EnablePCon      = 5;
     GP_EnableFSMonitor = 6;
+    GP_Max             = 6;
 #endif
 
 var
@@ -506,7 +507,7 @@ var
 #ifdef HAVE_EXPERIMENTAL_OPTIONS
     // Wizard page and variables for the experimental options.
     ExperimentalOptionsPage:TWizardPage;
-    RdbExperimentalOptions:array[GP_BuiltinDifftool..GP_EnableFSMonitor] of TCheckBox;
+    RdbExperimentalOptions:array[GP_BuiltinDifftool..GP_Max] of TCheckBox;
 #endif
 
     // Mapping controls to hyperlinks
@@ -2549,6 +2550,7 @@ function ShouldSkipPage(PageID:Integer):Boolean;
 var
     Msg,Cmd,StdOut,StdErr:String;
     Res:DWORD;
+    i:Integer;
 begin
     if (ProcessesPage<>NIL) and (PageID=ProcessesPage.ID) then begin
         // This page is only reached forward (by pressing "Next", never by pressing "Back").
@@ -2577,6 +2579,14 @@ begin
             Result:=False
         else
             Result:=(PageID<>wpInfoBefore) and (PageID<>wpFinished);
+#ifdef HAVE_EXPERIMENTAL_OPTIONS
+    // Skip experimental options page if all options are hidden
+    end else if (PageID=ExperimentalOptionsPage.ID) then begin
+        Result:=True;
+        for i:=1 to GP_Max do
+            if (RdbExperimentalOptions[i]<>nil) and RdbExperimentalOptions[i].Visible then
+                Result:=False;
+#endif
     end else
         Result:=False;
 #ifdef DEBUG_WIZARD_PAGE