lib: call Curl_strntolower instead of doing crafted loops

Closes #13627

lib/hostip.c

@@ -167,17 +167,12 @@ create_hostcache_id(const char *name,
                     int port, char *ptr, size_t buflen)
 {
   size_t len = nlen ? nlen : strlen(name);
-  size_t olen = 0;
   DEBUGASSERT(buflen >= MAX_HOSTCACHE_LEN);
   if(len > (buflen - 7))
     len = buflen - 7;
   /* store and lower case the name */
-  while(len--) {
-    *ptr++ = Curl_raw_tolower(*name++);
-    olen++;
-  }
-  olen += msnprintf(ptr, 7, ":%u", port);
-  return olen;
+  Curl_strntolower(ptr, name, len);
+  return msnprintf(&ptr[len], 7, ":%u", port) + len;
 }
 
 struct hostcache_prune_data {

lib/urlapi.c

@@ -234,10 +234,8 @@ size_t Curl_is_absolute_url(const char *url, char *buf, size_t buflen,
     /* the length of the scheme is the name part only */
     size_t len = i;
     if(buf) {
+      Curl_strntolower(buf, url, i);
       buf[i] = 0;
-      while(i--) {
-        buf[i] = Curl_raw_tolower(url[i]);
-      }
     }
     return len;
   }