Ignore configuration if it contains an empty vBucketMap

It is possible (although a bug...that is being fixed) to receive a configuration that contains an empty vBucketMap. Currently the SDK does not ignore these configurations which leaves the SDK susceptible to crashing if operations are attempted prior to updating the config. Specifically, floating point exceptions due to modulus operations w/ 0 in the denominator have been seen in wrapper SDKs (see code references here and here).

Lets add checks in when updating configuration to ignore configs that meet the condition: config.vbmap && config.vbmap->size() == 0.