[SMTChecker] Fix rational number short circuit

test/libsolidity/smtCheckerTests/operators/bitwise_rational_1.sol

@@ -0,0 +1,12 @@
+pragma experimental SMTChecker;
+
+contract C {
+	function f() public pure {
+		uint x = uint(~1);
+		// This assertion fails because type conversion is still unsupported.
+		assert(x == 2**256 - 2);
+		assert(~1 == -2);
+	}
+}
+// ----
+// Warning 6328: (169-192): Assertion violation happens here

test/libsolidity/smtCheckerTests/operators/bitwise_rational_2.sol

@@ -0,0 +1,15 @@
+pragma experimental SMTChecker;
+
+contract C {
+	function f() public pure {
+		assert(~1 | (~0xff & 0) == -2);
+		int x = ~1 | (~0xff ^ 0);
+		/// Result is negative, assertion fails.
+		assert(x > 0);
+		int y = ~x | (0xff & 1);
+		assert(y > 0);
+		assert(y & (0xffffffffffffffffff & 1) == 1);
+	}
+}
+// ----
+// Warning 6328: (181-194): Assertion violation happens here