Fix: Dangerzone installed using an msi built with WiX Toolset v3 is …

…not uninstalled by an msi built with WiX Toolset v5

Workaround for an issue after upgrading from WiX Toolset v3 to v5 where the previous
version of Dangerzone is not uninstalled during the upgrade by checking if the older installation
exists in "C:\Program Files (x86)\Dangerzone".

Also handle a special case for Dangerzone 0.8.0 which allows choosing the install location
during install by checking if the registry key for it exists.

Note that this seems to allow installing Dangerzone 0.8.0 after installing Dangerzone from this branch.
In this case the installer errors until Dangerzone 0.8.0 is uninstalled again

install/windows/build-wxs.py

@@ -177,6 +177,41 @@ def main():
     )
     ET.SubElement(ui_el, "UIRef", Id="WixUI_ErrorProgressText")
 
+    # Workaround for an issue after upgrading from WiX Toolset v3 to v5 where the previous
+    # version of Dangerzone is not uninstalled during the upgrade by checking if the older installation
+    # exists in "C:\Program Files (x86)\Dangerzone".
+    #
+    # Also handle a special case for Dangerzone 0.8.0 which allows choosing the install location
+    # during install by checking if the registry key for it exists.
+    #
+    # Note that this seems to allow installing Dangerzone 0.8.0 after installing Dangerzone from this branch.
+    # In this case the installer errors until Dangerzone 0.8.0 is uninstalled again
+    #
+    # TODO: Revert this once we are reasonably certain there aren't too many affected Dangerzone installations.
+    property_el = ET.SubElement(package_el, "Property", Id="OLDDANGERZONEFOUND")
+    dir_search_el = ET.SubElement(
+        property_el,
+        "DirectorySearch",
+        Id="dangerzone_install_folder",
+        Path="C:\\Program Files (x86)\\Dangerzone",
+    )
+    registry_search_el = ET.SubElement(package_el, "Property", Id="DANGERZONE080FOUND")
+    ET.SubElement(
+        registry_search_el,
+        "RegistrySearch",
+        Root="HKLM",
+        Key="SOFTWARE\\WOW6432Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\{03C2D2B2-9955-4AED-831F-DA4E67FC0FDB}",
+        Name="DisplayName",
+        Type="raw",
+    )
+    ET.SubElement(dir_search_el, "FileSearch", Name="dangerzone.exe")
+    ET.SubElement(
+        package_el,
+        "Launch",
+        Condition="NOT OLDDANGERZONEFOUND AND NOT DANGERZONE080FOUND",
+        Message="A previous version of [ProductName] is already installed. Please uninstall it from Programs and Features before proceeding with the installation.",
+    )
+
     # Add the ProgramMenuFolder StandardDirectory
     programmenufolder_el = ET.SubElement(
         package_el,