[BUGFIX] EM: Configuration inlineToWindow does not default to 1

Default configuration for inlineToWindow is set to 1 in ext_conf_template.txt but
if localconf.php contains an incomplete definition for $TYPO3_CONF_VARS['EXT']['extConf']['em'],
it defaults to 0 instead.

Change-Id: I3df433e9f9ddf2b610e6eaad89333f03bba3e231
Fixes: #31271
Releases: 4.6
Reviewed-on: http://review.typo3.org/6318
Reviewed-by: Steffen Ritter
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers