Only delete dummy image files if they exist

See #237

packages/viz/src/viz.mjs

@@ -88,7 +88,9 @@ function createImageFiles(module, images) {
 
 function removeImageFiles(module, imageFilePaths) {
   for (const path of imageFilePaths) {
-    module.FS.unlink(path);
+    if (module.FS.analyzePath(path).exists) {
+      module.FS.unlink(path);
+    }
   }
 }
 

packages/viz/test/render.test.mjs

@@ -352,6 +352,55 @@ stop
       });
     });
 
+    it("accepts two images with the same name", function() {
+      const result = viz.render("graph { a[image=\"test.png\"] }", {
+        images: [
+          { name: "test.png", width: 300, height: 200 },
+          { name: "test.png", width: 300, height: 200 }
+        ]
+      });
+
+      assert.deepStrictEqual(result, {
+        status: "success",
+        output: `graph {
+	graph [bb="0,0,321.03,214.96"];
+	node [label="\\N"];
+	a	[height=2.9856,
+		image="test.png",
+		pos="160.51,107.48",
+		width=4.4587];
+}
+`,
+        errors: []
+      });
+    });
+
+    it("the same image can be used twice", function() {
+      const result = viz.render("graph { a[image=\"test.png\"]; b[image=\"test.png\"] }", {
+        images: [
+          { name: "test.png", width: 300, height: 200 }
+        ]
+      });
+
+      assert.deepStrictEqual(result, {
+        status: "success",
+        output: `graph {
+	graph [bb="0,0,660.03,214.96"];
+	node [label="\\N"];
+	a	[height=2.9856,
+		image="test.png",
+		pos="160.51,107.48",
+		width=4.4587];
+	b	[height=2.9856,
+		image="test.png",
+		pos="499.51,107.48",
+		width=4.4587];
+}
+`,
+        errors: []
+      });
+    });
+
     it("accepts URLs for image names", function() {
       const result = viz.render("graph { a[image=\"http://example.com/test.png\"] }", {
         images: [