Fix possible double free in cli_command_name

Coverity indicates a possible double free in cli_command_name.  This
appears to be due to name being set to cli->commandname, and then if
this is not null name is freed, but cli->commandname is untouched.  If
this routine exits early (for example, the calloc fails), then
cli->commandname is now pointing to a freed memory block.

Fixed by ensuring that cli->commandname is freed and set to null if
not null already before assigning cli->commandname to name.

Author: Rob Sanders

libcli.c

@@ -163,12 +163,19 @@ static ssize_t _write(int fd, const void *buf, size_t count)
     }
     return written;
 }
+
 char *cli_command_name(struct cli_def *cli, struct cli_command *command)
 {
-    char *name = cli->commandname;
+    char *name;
     char *o;
 
-    if (name) free(name);
+    if (cli->commandname)
+    {
+        free(cli->commandname);
+        cli->commandname = NULL;
+    }
+    name = cli->commandname;
+
     if (!(name = calloc(1, 1)))
         return NULL;