[SMTChecker] Fix ICE implicit conversion string literal -> byte

test/libsolidity/smtCheckerTests/operators/slice_bytes.sol

@@ -0,0 +1,6 @@
+pragma experimental SMTChecker;
+contract C {
+	function f(bytes calldata b) external pure {
+		((b[:])[5]);
+	}
+}

test/libsolidity/smtCheckerTests/typecast/implicit_cast_string_literal_byte.sol

@@ -0,0 +1,16 @@
+pragma experimental SMTChecker;
+
+contract C {
+	mapping (byte => uint) map;
+	function f() public {
+		map[""] = 2;
+		uint x = map[""];
+		g("");
+		byte b = "";
+		assert(x == map[b]);
+		assert(x == map["x"]);
+	}
+	function g(byte b) internal pure {}
+}
+// ----
+// Warning 6328: (182-203): CHC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/typecast/string_literal_to_fixed_bytes_explicit.sol

@@ -0,0 +1,4 @@
+pragma experimental SMTChecker;
+contract SMT {
+	bytes32 constant internal NULL_BYTES32 = bytes32('');
+}