Prevent crashes from svg rendering

[hammerlink]

When rendering certain SVGs, resvg::render can panic because resvg uses several assert! calls internally. This caused application crashes in Cosmic Desktop: pop-os/cosmic-epoch#2452

This patch wraps the render call in std::panic::catch_unwind. If resvg panics, the panic is caught and None is returned instead of crashing the app.

Example problematic SVG:

<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">                                                    
  <defs>                                                                                                             
    <filter id="specular" width="50" height="50">                                              
      <feSpecularLighting result="specular" lighting-color="white"                                                   
                          x="10" y="10" width="5" height="5">                                                        
        <fePointLight x="50" y="50" z="200"/>                                                                        
      </feSpecularLighting>                                                                                          
    </filter>                                                                                                        
  </defs>                                                                                                            
  <rect width="100" height="100" fill="blue" filter="url(#specular)"/>                                               
</svg>

[hecrj]

Isn't this a resvg bug?

[hecrj]

Thanks!

Changed it so that we still try to render the half-way drawn image. This should avoid constant cache misses and make any issue apparent to the user.

[hammerlink]

Isn't this a resvg bug?

Yeah, it is a resvg bug. I mainly pushed this because it’s causing random crashes on Cosmic Desktop right now, and the fix for this issue in resvg has been sitting open since August. The fix should come from resvg, but this at least stops apps from crashing. Thanks for merging it.