only check for system install if not silent

build/win32/code.iss

@@ -963,21 +963,23 @@ var
 begin
   Result := True;
 
-#if "user" == InstallTarget
-  #if "ia32" == Arch
-    #define IncompatibleArchRootKey "HKLM32"
-      #else
-    #define IncompatibleArchRootKey "HKLM64"
-  #endif
-
-  RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleTargetAppId}', 2, 38) + '_is1';
-
-  if RegKeyExists({#IncompatibleArchRootKey}, RegKey) then begin
-    if MsgBox('{#NameShort} is already installed on this system for all users. Are you sure you want to install it for this user?', mbConfirmation, MB_YESNO) = IDNO then begin
-      Result := false;
+  #if "user" == InstallTarget
+    #if "ia32" == Arch
+      #define IncompatibleArchRootKey "HKLM32"
+    #else
+      #define IncompatibleArchRootKey "HKLM64"
+    #endif
+
+    if not WizardSilent() then begin
+      RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleTargetAppId}', 2, 38) + '_is1';
+
+      if RegKeyExists({#IncompatibleArchRootKey}, RegKey) then begin
+        if MsgBox('{#NameShort} is already installed on this system for all users. Are you sure you want to install it for this user?', mbConfirmation, MB_YESNO) = IDNO then begin
+          Result := false;
+        end;
+      end;
     end;
-  end;
-#endif
+  #endif
 
   if Result and IsWin64 then begin
     RegKey := 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\' + copy('{#IncompatibleArchAppId}', 2, 38) + '_is1';