fix build by msvc, introduced in r3054

src/core/ngx_output_chain.c

diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index 592f14a..0e39258 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -346,7 +346,7 @@
         size = (size_t) bsize;
 
     } else {
-        size = ctx->alignment - size;
+        size = (size_t) ctx->alignment - size;
 
         if ((off_t) size > bsize) {
             size = (size_t) bsize;
@@ -421,7 +421,7 @@
          * userland buffer direct usage conjunctly with directio
          */
 
-        b->start = ngx_pmemalign(ctx->pool, size, ctx->alignment);
+        b->start = ngx_pmemalign(ctx->pool, size, (size_t) ctx->alignment);
         if (b->start == NULL) {
             return NGX_ERROR;
         }