[FIX] web_pwa_oca: Guess properly mimetype

It seems since 3bd0327d6d
that the mimetype detection is not working properly for not fully
compliant SVG.

Let's resave SVG for having a compatible one + add a pointer when the
mimetype doesn't conform.

web_pwa_oca/models/res_config_settings.py

@@ -128,7 +128,10 @@ class ResConfigSettings(models.TransientModel):
         if not pwa_icon_mimetype.startswith(
             "image/svg"
         ) and not pwa_icon_mimetype.startswith("image/png"):
-            raise exceptions.UserError(_("You can only upload SVG or PNG files"))
+            raise exceptions.UserError(
+                _("You can only upload SVG or PNG files. Found: %s.")
+                % pwa_icon_mimetype
+            )
         # Delete all previous records if we are writting new ones
         if pwa_icon_ir_attachments:
             pwa_icon_ir_attachments.unlink()