[SMTChecker] Fix handling of function calls where the function identifier is nested in a tuple.

test/libsolidity/smtCheckerTests/functions/functions_identifier_nested_tuple_1.sol

@@ -0,0 +1,15 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint x;
+	function f() public {
+		x = 0;
+		((inc))();
+		assert(x == 1); // should hold
+	}
+
+	function inc() internal returns (uint) {
+		require(x < 100);
+		return ++x;
+	}
+}

test/libsolidity/smtCheckerTests/functions/functions_identifier_nested_tuple_2.sol

@@ -0,0 +1,23 @@
+pragma experimental SMTChecker;
+
+library L {
+	struct S {
+		uint256[] data;
+	}
+	function f(S memory _s) internal pure returns (uint256) {
+		require(_s.data.length > 0);
+		return 42;
+	}
+}
+
+contract C {
+	using L for L.S;
+	function f() public pure returns (uint256 y) {
+		L.S memory x;
+		y = (x.f)();
+		assert(y == 42); // should hold
+	}
+}
+// ----
+// Warning 6031: (289-292): Internal error: Expression undefined for SMT solver.
+// Warning 6031: (289-292): Internal error: Expression undefined for SMT solver.