builder/virtualbox: error if version can't be detected [GH-488]

CHANGELOG.md

@@ -3,6 +3,7 @@
 BUG FIXES:
 
 * builder/all: timeout waiting for SSH connection is a failure. [GH-491]
+* builder/virtualbox: error if VirtualBox version cant be detected. [GH-488]
 
 ## 0.3.9 (October 2, 2013)
 

builder/virtualbox/driver.go

@@ -135,9 +135,10 @@ func (d *VBox42Driver) Version() (string, error) {
 
 	versionOutput := strings.TrimSpace(stdout.String())
 	log.Printf("VBoxManage --version output: %s", versionOutput)
+
 	versionRe := regexp.MustCompile("[^.0-9]")
 	matches := versionRe.Split(versionOutput, 2)
-	if len(matches) == 0 {
+	if len(matches) == 0 || matches[0] == "" {
 		return "", fmt.Errorf("No version found: %s", versionOutput)
 	}