fix: Handle missing HTTP_USER_AGENT in request

VIPSWeb/views.py

@@ -66,10 +66,11 @@ def index(request):
 
 # Serving settings for JavaScript
 def settings_js(request):
-    user_agent = request.META['HTTP_USER_AGENT']
+    user_agent = request.META.get('HTTP_USER_AGENT', None)
     user_is_ie = False
-    if user_agent.find("MSIE") >= 0 or user_agent.find("Trident") >= 0:
-            user_is_ie = True
+    if user_agent is not None:
+        if user_agent.find("MSIE") >= 0 or user_agent.find("Trident") >= 0:
+                user_is_ie = True
     context = {
         'crop_categories': CropCategory.get_crop_categories_from_vipslogic_as_text(),
         'user_is_ie':  user_is_ie,