gdb_server: assert to avoid malloc(0)

Change-Id: I6ae3e007f4aa768f8bc64de78351750138f12e53
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>
Reviewed-on: http://openocd.zylin.com/135
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Øyvind Harboe <oyvindharboe@gmail.com>

src/server/gdb_server.c

@@ -1061,6 +1061,8 @@ static int gdb_get_registers_packet(struct connection *connection,
 		reg_packet_size += reg_list[i]->size;
 	}
 
+	assert(reg_packet_size > 0);
+
 	reg_packet = malloc(DIV_ROUND_UP(reg_packet_size, 8) * 2);
 	reg_packet_p = reg_packet;