Handle inbalanced declaration of constants

The following code would create a panic condition:

const foo, bar = "some thing"

Fixes #84

rules/hardcoded_credentials.go

@@ -59,6 +59,10 @@ func (r *Credentials) matchGenDecl(decl *ast.GenDecl, ctx *gas.Context) (*gas.Is
 		if valueSpec, ok := spec.(*ast.ValueSpec); ok {
 			for index, ident := range valueSpec.Names {
 				if r.pattern.MatchString(ident.Name) {
+					// const foo, bar = "same value"
+					if len(valueSpec.Values) <= index {
+						index = len(valueSpec.Values) - 1
+					}
 					if _, ok := valueSpec.Values[index].(*ast.BasicLit); ok {
 						return gas.NewIssue(ctx, decl, r.What, r.Severity, r.Confidence), nil
 					}

rules/hardcoded_credentials_test.go

@@ -79,3 +79,22 @@ func TestHardcodedConstant(t *testing.T) {
 
 	checkTestResults(t, issues, 1, "Potential hardcoded credentials")
 }
+
+func TestHardcodedConstantMulti(t *testing.T) {
+	config := map[string]interface{}{"ignoreNosec": false}
+	analyzer := gas.NewAnalyzer(config, nil)
+	analyzer.AddRule(NewHardcodedCredentials(config))
+
+	issues := gasTestRunner(`
+		package samples
+
+		import "fmt"
+
+		const username, password = "secret"
+
+		func main() {
+			fmt.Println("Doing something with: ", username, password)
+		}`, analyzer)
+
+	checkTestResults(t, issues, 1, "Potential hardcoded credentials")
+}