Fixed group item class generation

[gerrieg]

For a group of Number:Temperature items, the group is generated incorrectly and the JRuleItems class cannot be compiled.

.items file:

Group gTemperature

Number:Temperature Item_1 (gTemperature)
Number:Temperature Item_2 (gTemperature)

generated JRuleItems class:

public static JRuleNumber:TemperatureGroupItem gTemperature;

gTemperature = JRuleItemRegistry.get("gTemperature", JRuleInternalNumber:TemperatureGroupItem.class);

This patch fixed it for me

[querdenker2k]

@gerrieg Could you please add a test for this, to be sure that the error not occurs again

[gerrieg]

I quickly looked at the test classes and I can't see where the test should be added. Do you have a hint or are you kind enough to add the test yourself? Unfortunately, I don't have the time to take a close look at everything.
Thank you!