[SMTChecker] Fix ICE in string literal to fixed bytes implicit conversion

test/libsolidity/smtCheckerTests/typecast/string_literal_to_fixed_bytes_function_call.sol

@@ -0,0 +1,14 @@
+pragma experimental SMTChecker;
+contract B {
+    function f() pure public {
+		g("0123456");
+	}
+    function g(bytes7 a) pure public {
+		assert(a == "0123456");
+		assert(a == "1234567");
+	}
+}
+// ----
+// Warning: (162-184): Assertion violation happens here
+// Warning: (136-158): Assertion violation happens here
+// Warning: (162-184): Assertion violation happens here

test/libsolidity/smtCheckerTests/typecast/string_literal_to_fixed_bytes_modifier.sol

@@ -0,0 +1,11 @@
+pragma experimental SMTChecker;
+contract B {
+    function f() mod2("0123456") pure public { }
+    modifier mod2(bytes7 a) {
+		assert(a == "0123456");
+		assert(a == "1234567");
+		_;
+	}
+}
+// ----
+// Warning: (152-174): Assertion violation happens here

test/libsolidity/smtCheckerTests/typecast/string_literal_to_fixed_bytes_return.sol

@@ -0,0 +1,12 @@
+pragma experimental SMTChecker;
+contract C {
+    function g() public pure returns (bytes32 val) { return "abc"; }
+    function f1() public pure returns (bytes32 val) { return g(); }
+
+	function a() public pure {
+		assert(f1() == "abc");
+		assert(f1() == "cde");
+	}
+}
+// ----
+// Warning: (238-259): Assertion violation happens here

test/libsolidity/smtCheckerTests/typecast/string_literal_to_fixed_bytes_return_multi.sol

@@ -0,0 +1,15 @@
+pragma experimental SMTChecker;
+contract C {
+    function h() public pure returns (bytes32 val, bytes3 val2) { return ("abc", "def"); }
+    function g() public pure returns (bytes32 val) { return "abc"; }
+    function f1() public pure returns (bytes32 val) { return g(); }
+    function f2() public pure returns (bytes32 val, bytes3 val2) { return h(); }
+
+	function a() public pure {
+		(bytes32 v1, bytes3 v2) = f2();
+		assert(v1 == "abc");
+		assert(v2 == "cde");
+	}
+}
+// ----
+// Warning: (442-461): Assertion violation happens here