Locale (Linux): use environment variable if available

In some machine `setlocale(LC_MESSAGES, NULL)` returns `C` for some reason.

Author: CarterLi

src/detection/locale/locale_linux.c

@@ -4,6 +4,14 @@
 
 void ffDetectLocale(FFstrbuf* result)
 {
+    ffStrbufAppendS(result, getenv("LC_MESSAGES"));
+    if(result->length > 0)
+        return;
+
+    ffStrbufAppendS(result, getenv("LANG"));
+    if(result->length > 0)
+        return;
+
     #ifdef LC_MESSAGES
     ffStrbufAppendS(result, setlocale(LC_MESSAGES, NULL));