[5.x] Improve ImageGenerator Exception handling (#10786)

Co-authored-by: Jason Varga <jason@pixelfear.com>

src/Http/Controllers/CP/Assets/ThumbnailController.php

@@ -3,7 +3,9 @@
 namespace Statamic\Http\Controllers\CP\Assets;
 
 use Illuminate\Support\Facades\Cache;
+use League\Flysystem\UnableToReadFile;
 use League\Glide\Server;
+use Statamic\Exceptions\NotFoundHttpException;
 use Statamic\Facades\Asset;
 use Statamic\Facades\Config;
 use Statamic\Facades\Image;
@@ -110,6 +112,8 @@ private function generate()
                 $this->asset,
                 $preset ? ['p' => $preset] : []
             );
+        } catch (UnableToReadFile $e) {
+            throw new NotFoundHttpException;
         } finally {
             Cache::forget($this->mutex());
         }

src/Imaging/ImageGenerator.php

@@ -11,7 +11,6 @@
 use League\Glide\Server;
 use Statamic\Contracts\Assets\Asset;
 use Statamic\Events\GlideImageGenerated;
-use Statamic\Exceptions\NotFoundHttpException;
 use Statamic\Facades\Asset as Assets;
 use Statamic\Facades\Config;
 use Statamic\Facades\File;
@@ -258,7 +257,7 @@ private function generate($image)
         try {
             $path = $this->server->makeImage($image, $this->params);
         } catch (GlideFileNotFoundException $e) {
-            throw new NotFoundHttpException;
+            throw UnableToReadFile::fromLocation($image);
         }
 
         GlideImageGenerated::dispatch($path, $this->params);