Improved error handling

Author: neoneye

Source/TriangleDrawMain/Browser/BrowserViewController.swift

@@ -249,7 +249,7 @@ extension BrowserViewController: UIDocumentBrowserViewControllerDelegate {
 			log.error("documentURL: '\(documentURL)'  error: nil")
 		}
 
-        // Show an error to the user
+        // Show the error to the user
         let errorMessage: String = error.map { "\($0)" } ?? "The error is 'nil'. No info provided."
         let alert = UIAlertController(title: "Error in failedToImportDocumentAt", message: errorMessage, preferredStyle: .alert)
         let action = UIAlertAction(title: "OK", style: .default) { (_) in }

Source/TriangleDrawMain/Main/AppDelegate.swift

@@ -122,9 +122,14 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
 				return
 			}
 
+            guard let url = revealedDocumentURL else {
+                log.error("revealDocument. No URL revealed. inputURL \(inputURL)")
+                return
+            }
+
 			// Present the Document View Controller for the revealed URL.
 			browserViewController.presentDocument(
-				at: revealedDocumentURL!,
+				at: url,
 				animated: true,
 				displayNameBehavior: .extractFromURL
 			)