Remove duplicated code from isOK

Author: kean

Sources/SwiftSQL/SQLConnection.swift

@@ -111,7 +111,7 @@ public final class SQLConnection {
     // MARK: Private
 
     @discardableResult
-    private func isOK(_ code: Int32) throws -> Int32 {
+    func isOK(_ code: Int32) throws -> Int32 {
         guard let error = SQLError(code: code, db: ref) else { return code }
         throw error
     }

Sources/SwiftSQL/SQLStatement.swift

@@ -217,7 +217,6 @@ public final class SQLStatement {
 
     @discardableResult
     private func isOK(_ code: Int32) throws -> Int32 {
-        guard let error = SQLError(code: code, db: db.ref) else { return code }
-        throw error
+        try db.isOK(code)
     }
 }