[FIX] http_routing: restrict lang matching to installed lang

When accessing an URL, there is some computation to check if you try to access
a lang. Part of this job is to get the closest language available.
For instance, you could try to get `/fr_BE/..` and it would redirect to
`/fr_FR/..` if french is installed but not belgian french.

There is a known issue when loading files/assets from a module starting by the
same letter than a lang, in debug assets.
Only reported case was `hr_XXX` modules which would be redirected to `hr_HR`
lang (croatian).

So, the issue would only occur when:
1. Debug assets is enabled
2. hr_HR lang is activated
3. only hr_XX modules would be impacted

But since 269aa59411, the issue would appear even if `hr_HR` was not activated.

This commit restore the issue to its minimal case, when `hr_HR` lang is
activated.

closes odoo/odoo#37494

Signed-off-by: Olivier Dony (odo) <odo@openerp.com>

addons/http_routing/models/ir_http.py

@@ -302,11 +302,11 @@ class IrHttp(models.AbstractModel):
         """ Try to find a similar lang. Eg: fr_BE and fr_FR
             :param lang_code: the lang `code` (en_US)
         """
-        short_match = False
         if not lang_code:
-            return short_match
+            return False
+        short_match = False
         short = lang_code.partition('_')[0]
-        for code in [code for code, _, _ in request.env['res.lang'].get_available()]:
+        for (code, _) in request.env['res.lang'].get_installed():
             if code == lang_code:
                 return code
             if not short_match and code.startswith(short):