Only print the clean number menu when needed

The input is only asked when needed, but the numbered package list was
still printed either way. This fixes it so the list is not shown unless
needed.

install.go

@@ -175,13 +175,15 @@ func install(parser *arguments) error {
 	}
 
 	if config.CleanMenu {
-		askClean := pkgbuildNumberMenu(do.Aur, remoteNamesCache)
-		toClean, err := cleanNumberMenu(do.Aur, remoteNamesCache, askClean)
-		if err != nil {
-			return err
-		}
+		if anyExistInCache(do.Aur) {
+			askClean := pkgbuildNumberMenu(do.Aur, remoteNamesCache)
+			toClean, err := cleanNumberMenu(do.Aur, remoteNamesCache, askClean)
+			if err != nil {
+				return err
+			}
 
-		cleanBuilds(toClean)
+			cleanBuilds(toClean)
+		}
 	}
 
 	toSkip := pkgbuildsToSkip(do.Aur, targets)
@@ -485,6 +487,19 @@ func parsePackageList(dir string) (map[string]string, string, error) {
 	return pkgdests, version, nil
 }
 
+func anyExistInCache(bases []Base) bool {
+	for _, base := range bases {
+		pkg := base.Pkgbase()
+		dir := filepath.Join(config.BuildDir, pkg)
+
+		if _, err := os.Stat(dir); !os.IsNotExist(err) {
+			return true
+		}
+	}
+
+	return false
+}
+
 func pkgbuildNumberMenu(bases []Base, installed stringSet) bool {
 	toPrint := ""
 	askClean := false