cast argument as unsigned

Author: airween

src/request_body_processor/multipart.cc

@@ -362,11 +362,11 @@ int Multipart::parse_content_disposition(const char *c_d_value, int offset) {
             const char* start_of_filename = p;
             while ((*p != '\0') && (*p != ';')) {
                 if (*p == '%') {
-                    if ((*(p+1) == '\0') || (!isxdigit(*(p+1))) || (*(p+2) == '\0') || (!isxdigit(*(p+2)))) {
+                    if ((*(p+1) == '\0') || (!isxdigit(*(p+1))) || (*(p+2) == '\0') || (!isxdigit(static_cast<unsigned char>(*(p+2))))) {
                         return -18;
                     }
                     p += 3;
-                } else if (isalnum(*p) || strchr(attr_char_special, *p)) {
+                } else if (isalnum(static_cast<unsigned char>(*p)) || strchr(attr_char_special, *p)) {
                     p++;
                 } else {
                     return -19;