Preinitialize the sockaddr_un variable to zero

Don't pass random sun_len for the BSD's,
zero the whole structure as recommended for portability.

Reported by Coverity.

gdbsupport/ChangeLog:

	* agent.cc (gdb_connect_sync_socket): Preinitialize addr with zeros.

gdbsupport/ChangeLog

@@ -1,3 +1,7 @@
+2020-10-01  Kamil Rytarowski  <n54@gmx.com>
+
+	* agent.cc (gdb_connect_sync_socket): Preinitialize addr with zeros.
+
 2020-09-29  Pedro Alves  <pedro@palves.net>
 
 	* valid-expr.h (CHECK_VALID_EXPR_INT): Make archetype a template
@@ -327,4 +331,3 @@
 	* acinclude.m4, aclocal.m4, config.in, configure, configure.ac,
 	Makefile.am, Makefile.in, README: New files.
 	* Moved from ../gdb/gdbsupport/
-

gdbsupport/agent.cc

@@ -138,7 +138,7 @@ static int
 gdb_connect_sync_socket (int pid)
 {
 #ifdef HAVE_SYS_UN_H
-  struct sockaddr_un addr;
+  struct sockaddr_un addr = {};
   int res, fd;
   char path[UNIX_PATH_MAX];