Core: removed meaningless check from ngx_palloc_block().

The check became meaningless after refactoring in 2a92804f4109.
With the loop currently in place, "current" can't be NULL, hence
the check can be dropped.

Additionally, the local variable "current" was removed to
simplify code, and pool->current now used directly instead.

Found by Coverity (CID 714236).

src/core/ngx_palloc.c

@@ -181,7 +181,7 @@ ngx_palloc_block(ngx_pool_t *pool, size_t size)
 {
     u_char      *m;
     size_t       psize;
-    ngx_pool_t  *p, *new, *current;
+    ngx_pool_t  *p, *new;
 
     psize = (size_t) (pool->d.end - (u_char *) pool);
 
@@ -200,18 +200,14 @@ ngx_palloc_block(ngx_pool_t *pool, size_t size)
     m = ngx_align_ptr(m, NGX_ALIGNMENT);
     new->d.last = m + size;
 
-    current = pool->current;
-
-    for (p = current; p->d.next; p = p->d.next) {
+    for (p = pool->current; p->d.next; p = p->d.next) {
         if (p->d.failed++ > 4) {
-            current = p->d.next;
+            pool->current = p->d.next;
         }
     }
 
     p->d.next = new;
 
-    pool->current = current ? current : new;
-
     return m;
 }