Stop special-casing the (very unlikely) "no /XObject found"-scenario, when parsing OPS.paintXObject operators, in PartialEvaluator.{getOperatorList, getTextContent}

Originally there weren't any (generally) good ways to handle errors gracefully, on the worker-side, however that's no longer the case and we can simply fallback to the existing `ignoreErrors` functionality instead.
Also, please note that the "no `/XObject` found"-scenario should be *extremely* unlikely in practice and would only occur in corrupt/broken documents.

Note that the `PartialEvaluator.getOperatorList` case is especially bad currently, since we'll simply (attempt to) send the data as-is to the main-thread. This is quite bad, since in a corrupt/broken document the data *could* contain anything and e.g. be unclonable (which would cause breaking errors).
Also, we're (obviously) not attempting to do anything with this "raw" `OPS.paintXObject` data on the main-thread and simply ensuring that we never send it definately seems like the correct approach.

src/display/canvas.js

@@ -2433,10 +2433,6 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       this.ctx.fillRect(0, 0, 1, 1);
     },
 
-    paintXObject: function CanvasGraphics_paintXObject() {
-      warn("Unsupported 'paintXObject' command.");
-    },
-
     // Marked content
 
     markPoint: function CanvasGraphics_markPoint(tag) {