Don't cache /ExtGState entries that contain fonts (PR 12087 follow-up)

I completely overlooked the fact that `PartialEvaluator.handleSetFont` also updates the current `state`, which means that currently we're not actually handling font data correctly for cached /ExtGState data. (Thankfully, using /ExtGState to set a font is somewhat rare in practice.)

src/core/evaluator.js

@@ -846,6 +846,8 @@ class PartialEvaluator {
           gStateObj.push([key, value]);
           break;
         case "Font":
+          isSimpleGState = false;
+
           promise = promise.then(() => {
             return this.handleSetFont(
               resources,