Fix behaviour of app.alert() with a single object argument.

testing/resources/javascript/app_alert.in

 {{header}}
 {{object 1 0}} <<
   /Type /Catalog
   /Pages 2 0 R
   /OpenAction 10 0 R
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 endobj
 {{object 2 0}} <<
   /Type /Pages
   /Count 1
@@ skipping 17 matching lines @@
   /Type /Action
   /S /JavaScript
   /JS 11 0 R
 >>
 endobj
 % JS program to exexute
 {{object 11 0}} <<
 >>
 stream
 app.alert("This test passes if alert() logs output under the test utility.");
+app.alert("message", 1, 2, "title");
+app.alert({"cMsg": "message", "cTitle": "title"});
+app.alert({"cMsg": "message", "cTitle": "title", "nIcon": 3, "nType": 4});
+app.alert(undefined);
+app.alert(null);
+app.alert(true);
+app.alert(false);
+app.alert(42);
+app.alert([1, 2, 3]);
+app.alert([1, 2, {"color": "red"}]);
+app.alert({"color": "red"}, 5, 6, "title"); 
+try {
+  app.alert();
+} catch (e) {
+  app.alert("Caught expected error " + e);
+}
+try {
+  app.alert({});
+} catch (e) {
+  app.alert("Caught expected error " + e);
+}
+try {
+  app.alert({"color": "red", "size": 42});
+} catch (e) {
+  app.alert("Caught expected error " + e);
+}
 endstream
 endobj
 {{xref}}
 trailer <<
   /Root 1 0 R
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 %%EOF