Fix #4914 by ignoring hidden annotation
Zero the height and width of the PageView canvas before deleting.
Return ErrorFont in loadFont when the fontRef is undefined
Merge pull request #4920 from nnethercote/zero-canvas-before-deleting

Zero the height and width of the PageView canvas before deleting.
Merge pull request #4922 from Snuffleupagus/undefined-fontRef

Return ErrorFont in loadFont when the fontRef is undefined
Merge pull request #4915 from dferer/fix-4914

Fix #4914