Fix resize issue in OutlinePass

[Julianouyang]

Related issue: #XXXX

Description

This PR fixes an issue when resolution is passed as 0x0. The resize function couldn't properly resize renderTargetDepthBuffer, and it certainly breaks the outline effect.

[Julianouyang]

Off-topic but for discussion:
I found some posts that complained OutlinePass not working with white background (because of the blending). In my app I added an option to turn off the hidden outline, by changing the related shader. It's also useful if users don't want to see the hidden outline. Let me know if this is worth sharing.

[mrdoob]

Thanks!