never close fd 0, 1 or 2 in buffer_close

buffer/buffer_close.c

@@ -2,6 +2,6 @@
 #include <unistd.h>
 
 void buffer_close(buffer* b) {
-  if (b->fd != -1) close(b->fd);
+  if (b->fd > 2) close(b->fd);
   if (b->deinit) b->deinit(b);
 }

buffer/buffer_frombuf.c

@@ -15,4 +15,5 @@ void buffer_frombuf(buffer* b,const char* x,size_t l) {
   b->a=l;
   b->fd=0;
   b->op=dummyreadwrite;
+  b->deinit=0;
 }

buffer/buffer_tosa.c

@@ -22,5 +22,6 @@ int buffer_tosa(buffer* b,stralloc* sa) {
   b->fd=0;
   b->op=strallocwrite;
   b->cookie=sa;
+  b->deinit=0;
   return 0;
 }

socket/fmt_ip6ifc.c

@@ -3,7 +3,7 @@
 #include "ip4.h"
 #include "ip6.h"
 
-unsigned int fmt_ip6ifc(char *s,const char ip[16],uint32 scope_id)
+size_t fmt_ip6ifc(char *s,const char ip[16],uint32 scope_id)
 {
   if (ip6_isv4mapped(ip))
     return fmt_ip4(s,ip+12);