style: satisfy wsl_v5 blank-line-before-defer rule

Insert the blank line wsl_v5 requires above four defer statements
whose deferred closure does not share a variable with the immediately
preceding line, across internal/handlers, internal/httpfetcher, and
internal/imgcache. No behavior change.

internal/httpfetcher/httpfetcher_internal_test.go

@@ -237,6 +237,7 @@ func TestMockFetcher_FetchesFile(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Fetch() error = %v", err)
 	}
+
 	defer func() { _ = result.Content.Close() }()
 
 	if result.ContentType != contentTypeJPEG {