#6030: Remove an assert that fires when parsing an invalid shader exp…

…ression in material stages. This is user input and can occur rather frequently when manually editing materials.

radiantcore/shaders/ShaderExpression.cpp

@@ -225,8 +225,6 @@ class ShaderExpressionParser
 		auto rv = operands.top();
 		operands.pop();
 
-		assert(operands.empty()); // there should be nothing left on the stack
-
 		return rv;
 	}