urlapi: part of conditional expression is always true: (relurl[0] == '/')

Fixes warning detected by PVS-Studio
Fixes #4374

lib/urlapi.c

@@ -351,7 +351,7 @@ static char *concat_url(const char *base, const char *relurl)
   else {
     /* We got a new absolute path for this server */
 
-    if((relurl[0] == '/') && (relurl[1] == '/')) {
+    if(relurl[1] == '/') {
       /* the new URL starts with //, just keep the protocol part from the
          original one */
       *protsep = 0;