Fixed excessive memory usage while parsing configuration.

The b->pos points to the next symbol here.

Reported by ilexshen.

src/core/ngx_conf_file.c

@@ -680,7 +680,7 @@ ngx_conf_read_token(ngx_conf_t *cf)
                     return NGX_ERROR;
                 }
 
-                word->data = ngx_pnalloc(cf->pool, b->pos - start + 1);
+                word->data = ngx_pnalloc(cf->pool, b->pos - 1 - start + 1);
                 if (word->data == NULL) {
                     return NGX_ERROR;
                 }