internal/cmd/avogen: write output file even when gofmt fails (#165)

This makes it easier to debug avogen: when you emit invalid syntax, you can inspect the generated file to determine what went wrong, instead of having only gofmt's error to work with.

internal/cmd/avogen/main.go

@@ -73,13 +73,14 @@ func main() {
 	}
 
 	// Generate output.
-	b, err := g.Generate(is)
+	b, generr := g.Generate(is)
-	if err != nil {
-		log.Fatal(err)
-	}
 
 	// Write.
 	if _, err := w.Write(b); err != nil {
 		log.Fatal(err)
 	}
+
+	if generr != nil {
+		log.Fatal(generr)
+	}
 }

internal/gen/gen.go

@@ -30,6 +30,10 @@ func GoFmt(i Interface) Interface {
 		if err != nil {
 			return nil, err
 		}
-		return format.Source(b)
+		formatted, err := format.Source(b)
+		if err != nil {
+			return b, err
+		}
+		return formatted, nil
 	})
 }