Add check for EXIF data existence in Object/Image

- Addresses https://github.com/friendica/friendica/issues/6338#issuecomment-467121955

src/Object/Image.php

@@ -447,7 +447,7 @@ class Image
 			return;
 		}
 
-		$ort = $exif['IFD0']['Orientation'];
+		$ort = isset($exif['IFD0']['Orientation']) ? $exif['IFD0']['Orientation'] : 1;
 
 		switch ($ort) {
 			case 1: // nothing