Regression: "backdrop" in editorSettings may not be defined

[indigoxela]

The (rare) problem has been introduced with #143, where a check is done for a format.editorSettings.backdrop.allowInlineStyle setting.

But "backdrop" doesn't exist if the profile doesn't use any plugin that provides own settings.

This results in the editor not initializing at all with: Uncaught (in promise) TypeError: format.editorSettings.backdrop is undefined

To fix this, just do a check if the item exists before trying to access it.

[indigoxela]

Reopening this issue, as the yesterday's fix contains a logic flaw.