Added if...else-statement for $query

Added if...else statement following WordPress Codex for WP_Query
(http://codex.wordpress.org/Class_Reference/WP_Query) to resolve a
notice (Undefined variable: options) in \meta-box\inc\fields\post.php on
line 150 and a warning (Invalid argument supplied for foreach()) in
\meta-box\inc\fields\select.php on line 132 in case $query is empty.
Merge pull request #396 from studify/master

Added if...else-statement for $query