[+BUGFIX] Fluid (Core): Boolean expressions can now contain negative numbers. Resolves #9434.

Boolean expressions with negative numbers did not work so far.
Now, they work as expected. Example from Viewhelpertest which displayed
a wrong result before, and now displays the correct result:

<f:if condition="{testVariables.number.minusOne} < -1.1">
	<f:then>Then part!</f:then>
	<f:else>Else part!</f:else>
</f:if>

Issue: #9434