locale: fix environment checks: LC_ALL has precedence over LC_CTYPE 'man 7 locale' describes following precedence: If the second argument to setlocale(3) is an empty string, "", for the default locale, it is determined using the following steps: 1. If there is a non-null environment variable LC_ALL, the value of LC_ALL is used. 2. If an environment variable with the same name as one of the categories above exists and is non-null, its value is used for that category. 3. If there is a non-null environment variable LANG, the value of LANG is used. So, if LC_ALL is set, it is used regardless of LC_CTYPE or LANG. Hence, when suggesting users what to change when their locale is invalid, we should also first check LC_ALL instead of LC_CTYPE.