Fix for issue #3826 (ldapsearch doesn't prompt bind password when the option -w is not provided)
The behavior modification was introduced in rev #4956 in the following method:
org.opends.server.tools.LDAPConnection.connectToHost()

In the old version (rev #3847 line #291) , the bindPW was set to null.
In the new version (rev #4956 line #307), the bindPW is set to an empty ByteString

The actual bind, handled by LDAPAuthenticationHandler.doSimpleBind() method,
switches in interactive mode when bindPW is null, which is not the case with the
new version.

We now also check to the bind password in an empty ByteString.