Add regression test for negative LW normalization in gs operator

Ensure that negative “LW” entries in an ExtGState dictionary are converted to their absolute values when the “gs” operator is processed.

See PR https://github.com/mozilla/pdf.js/pull/19639

test/unit/evaluator_spec.js

@@ -423,4 +423,30 @@ describe("evaluator", function () {
       expect(operatorList.length).toEqual(0);
     });
   });
+
+  describe("graphics-state operators", function () {
+    it("should convert negative line width to absolute value in the graphic state", async function () {
+      const gState = new Dict();
+      gState.set("LW", -5);
+      const extGState = new Dict();
+      extGState.set("GSneg", gState);
+
+      const resources = new ResourcesMock();
+      resources.ExtGState = extGState;
+
+      const stream = new StringStream("/GSneg gs");
+      const result = await runOperatorListCheck(
+        partialEvaluator,
+        stream,
+        resources
+      );
+
+      expect(result.fnArray).toEqual([OPS.setGState]);
+
+      const stateEntries = result.argsArray[0][0];
+      const lwEntry = stateEntries.find(([key]) => key === "LW");
+      expect(lwEntry).toBeDefined();
+      expect(lwEntry[1]).toEqual(5);
+    });
+  });
 });