Fix ctype(3) function arguments.

Valid are unsigned char and EOF; add cast to make sure we're in the
allowed range.

i3-config-wizard/main.c

@@ -732,7 +732,7 @@ static void finish(void) {
 
         /* Skip leading whitespace */
         char *walk = line;
-        while (isspace(*walk) && walk < (line + len)) {
+        while (isspace((unsigned char)*walk) && walk < (line + len)) {
             /* Pre-output the skipped whitespaces to keep proper indentation */
             fputc(*walk, ks_config);
             walk++;

i3bar/src/child.c

@@ -525,7 +525,7 @@ static void stdin_io_first_line_cb(int fd) {
 
 static bool isempty(char *s) {
     while (*s != '\0') {
-        if (!isspace(*s)) {
+        if (!isspace((unsigned char)*s)) {
             return false;
         }
         s++;

src/util.c

@@ -67,7 +67,7 @@ __attribute__((__const__)) bool rect_equals(const Rect a, const Rect b) {
 __attribute__((pure)) bool name_is_digits(const char *name) {
     /* positive integers and zero are interpreted as numbers */
     for (size_t i = 0; i < strlen(name); i++) {
-        if (!isdigit(name[i])) {
+        if (!isdigit((unsigned char)name[i])) {
             return false;
         }
     }