a couple of fixes to prevent crashing if package has no files (e.g., go.mod not set properly)

Author: Randall C. O'Reilly

cmd_build.go

@@ -74,12 +74,12 @@ func gopyRunCmdBuild(cmdr *commander.Command, args []string) error {
 			return fmt.Errorf("gopy-gen: go build / load of package failed with path=%q: %v", path, err)
 		}
 		pkg, err := parsePackage(bpkg)
-		if cfg.Name == "" {
-			cfg.Name = pkg.Name()
-		}
 		if err != nil {
 			return err
 		}
+		if cfg.Name == "" {
+			cfg.Name = pkg.Name()
+		}
 	}
 	return runBuild("build", cfg)
 }

gen.go

@@ -122,6 +122,11 @@ func loadPackage(path string, buildFirst bool) (*packages.Package, error) {
 }
 
 func parsePackage(bpkg *packages.Package) (*bind.Package, error) {
+	if len(bpkg.GoFiles) == 0 {
+		err := fmt.Errorf("gopy: no files in package %q", bpkg.PkgPath)
+		fmt.Println(err)
+		return nil, err
+	}
 	dir, _ := filepath.Split(bpkg.GoFiles[0])
 	p := bpkg.Types