Fix coverity defects: zfs channel programs

CID 173243, 173245:  Memory - corruptions  (OVERRUN)
 Added size argument to lcompat_sprintf() to avoid use of INT_MAX

CID 173244:  Integer handling issues  (OVERFLOW_BEFORE_WIDEN)
 Added cast to uint64_t to avoid a 32 bit overflow warning

CID 173242:  Integer handling issues  (CONSTANT_EXPRESSION_RESULT)
 Conditionally removed unused luai_numisnan() floating point check

CID 173241:  Resource leaks  (RESOURCE_LEAK)
 Added missing close(fd) on error path

CID 173240:    (UNINIT)
Fixed uninitialized variable in get_special_prop()

CID 147560:  Null pointer dereferences  (NULL_RETURNS)
Cleaned up bad code merge in dsl_dataset_promote_check()

CID 28475:  Memory - illegal accesses  (OVERRUN)
Fixed lcompat_sprintf() to use a size paramater

CID 28418, 28422:  Error handling issues  (CHECKED_RETURN)
Added function result cast to (void) to avoid warning

CID 23935, 28411, 28412:  Memory - corruptions  (ARRAY_VS_SINGLETON)
Added casts to avoid exposing result as an array

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <don.brady@delphix.com>
Closes #7181

cmd/zfs/zfs_main.c

@@ -7275,6 +7275,8 @@ zfs_do_channel_program(int argc, char **argv)
 	if ((zhp = zpool_open(g_zfs, poolname)) == NULL) {
 		(void) fprintf(stderr, gettext("cannot open pool '%s'"),
 		    poolname);
+		if (fd != 0)
+			(void) close(fd);
 		return (1);
 	}
 	zpool_close(zhp);