Fix parseDSNSettings with bad backslash

fixes #49

config.go

@@ -506,6 +506,9 @@ func parseDSNSettings(s string) (map[string]string, error) {
 				}
 				if s[end] == '\\' {
 					end++
+					if end == len(s) {
+						return nil, errors.New("invalid backslash")
+					}
 				}
 			}
 			val = strings.Replace(strings.Replace(s[:end], "\\\\", "\\", -1), "\\'", "'", -1)

config_test.go

@@ -539,6 +539,13 @@ func TestParseConfigDSNLeadingEqual(t *testing.T) {
 	require.Error(t, err)
 }
 
+// https://github.com/jackc/pgconn/issues/49
+func TestParseConfigDSNTrailingBackslash(t *testing.T) {
+	_, err := pgconn.ParseConfig(`x=x\`)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid backslash")
+}
+
 func TestConfigCopyReturnsEqualConfig(t *testing.T) {
 	connString := "postgres://jack:secret@localhost:5432/mydb?application_name=pgxtest&search_path=myschema&connect_timeout=5"
 	original, err := pgconn.ParseConfig(connString)