[SMTChecker] Fix ICE when using >>>

test/libsolidity/smtCheckerTests/operators/shifts/shr_unused.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	function f() public pure {
+		fixed x;
+		assert(x >>> 6 == 0);
+	}
+}
+// ----
+// UnimplementedFeatureError: Not yet implemented - FixedPointType.