Fixed counting of sent bytes in the send chain functions on EINTR.

Previously, a value of the "send" variable wasn't properly adjusted
in a rare case when syscall was interrupted by a signal.  As a result,
these functions could send less data than the limit allows.

src/os/unix/ngx_darwin_sendfile_chain.c

@@ -308,6 +308,7 @@ ngx_darwin_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
         in = ngx_handle_sent_chain(in, sent);
 
         if (eintr) {
+            send = prev_send + sent;
             continue;
         }
 

src/os/unix/ngx_freebsd_sendfile_chain.c

@@ -378,6 +378,7 @@ ngx_freebsd_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
         }
 
         if (eintr) {
+            send = prev_send + sent;
             continue;
         }
 

src/os/unix/ngx_linux_sendfile_chain.c

@@ -316,6 +316,7 @@ ngx_linux_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
         in = ngx_handle_sent_chain(in, sent);
 
         if (eintr) {
+            send = prev_send;
             continue;
         }
 

src/os/unix/ngx_solaris_sendfilev_chain.c

@@ -200,6 +200,7 @@ ngx_solaris_sendfilev_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
         in = ngx_handle_sent_chain(in, sent);
 
         if (eintr) {
+            send = prev_send + sent;
             continue;
         }
 

src/os/unix/ngx_writev_chain.c

@@ -134,6 +134,7 @@ ngx_writev_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
         in = ngx_handle_sent_chain(in, sent);
 
         if (eintr) {
+            send = prev_send;
             continue;
         }