[fenix] For https://github.com/mozilla-mobile/fenix/issues/7522 Catch IllegalArgumentException when validating search string

app/src/main/java/org/mozilla/fenix/settings/search/AddSearchEngineFragment.kt

@@ -171,8 +171,7 @@ class AddSearchEngineFragment : Fragment(), CompoundButton.OnCheckedChangeListen
         custom_search_engine_search_string_field.error = when {
             searchString.isEmpty() ->
                 resources.getString(R.string.search_add_custom_engine_error_empty_search_string)
-            !searchString.contains("%s")
+            !searchString.contains("%s") ->
-                    || !searchString.contains("http") ->
                 resources.getString(R.string.search_add_custom_engine_error_missing_template)
             else -> null
         }

app/src/main/java/org/mozilla/fenix/settings/search/SearchStringValidator.kt

@@ -20,6 +20,8 @@ object SearchStringValidator {
             client.fetch(request)
         } catch (e: IOException) {
             return Result.CannotReach
+        } catch (e: IllegalArgumentException) {
+            return Result.CannotReach
         }
 
         // read the response stream to ensure the body is closed correctly. workaround for https://bugzilla.mozilla.org/show_bug.cgi?id=1603114