[UWP] [Export] added additional checks for blank values

`Short Name` and `Publisher Display Name` are mandatory.
You can't even sign the app package without them in the manifest.

platform/uwp/export/export.cpp

@@ -1144,11 +1144,21 @@ public:
 			return valid;
 		}
 
+		if (!_valid_resource_name(p_preset->get("package/short_name"))) {
+			valid = false;
+			err += TTR("Invalid package short name.") + "\n";
+		}
+
 		if (!_valid_resource_name(p_preset->get("package/unique_name"))) {
 			valid = false;
 			err += TTR("Invalid package unique name.") + "\n";
 		}
 
+		if (!_valid_resource_name(p_preset->get("package/publisher_display_name"))) {
+			valid = false;
+			err += TTR("Invalid package publisher display name.") + "\n";
+		}
+
 		if (!_valid_guid(p_preset->get("identity/product_guid"))) {
 			valid = false;
 			err += TTR("Invalid product GUID.") + "\n";