Fix gen_wc8bit support for finding a UTF8 locale on host.

gen_wc8bit was previously patched to support UTF8 locales other than the
default en_US.UTF-8 by patch id 0e14b8f425c562749d3821a42414b1ce6b3b0923.

This was incomplete in its implementation and still failed where item(s)
in the list returned by 'locale -a' already had 'UTF8' appended to the
name. This patch rectifies this situation, plus adds an extra fix to
avoid trimming '\n' from an empty line which could cause a segfault.

Signed-off-by: Andy Gibbs <andyg1001@hotmail.co.uk>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

extra/locale/gen_wc8bit.c

@@ -112,9 +112,10 @@ int main(int argc, char **argv)
 				goto locale_failure;
 
 			len = strlen(buf);
-			if (buf[len - 1] == '\n')
+			if (len > 0 && buf[len - 1] == '\n')
 				buf[--len] = '\0';
-			strcat(buf, ".UTF8");
+			if (len < 5 || strcasecmp(&buf[len-5], ".UTF8") != 0)
+				strcat(buf, ".UTF8");
 			if (setlocale(LC_CTYPE, buf))
 				goto locale_success;
 		}