N°5588 - Improve PDF export robustness when AttributeImage dimensions cannot be determined (#350)

Can happen for example on SVG images
Now the export won't crash anymore, and we'll get a log (export channel, warning level) with  the object and attribute causing a problem as context

Co-authored-by: Molkobain <lajarige.guillaume@free.fr>

core/log.class.inc.php

@@ -549,6 +549,12 @@ class LogChannels
 
 	const DEADLOCK = 'DeadLock';
 
+	/**
+	 * @var string
+	 * @since 2.7.9
+	 */
+	const EXPORT = 'export';
+
 	const INLINE_IMAGE = 'InlineImage';
 
 	/**