[SMTChecker] Fix calls to virtual/overriden functions

test/libsolidity/smtCheckerTests/functions/virtual_function_assert.sol

@@ -0,0 +1,21 @@
+pragma experimental SMTChecker;
+contract A {
+    int x = 0;
+
+    function f() virtual internal view {
+        assert(x == 0);
+    }
+
+    function proxy() public view {
+        f();
+    }
+}
+
+contract C is A {
+
+    function f() internal view override {
+        assert(x == 1);
+    }
+}
+// ----
+// Warning 6328: (259-273): CHC: Assertion violation happens here.\nCounterexample:\nx = 0\n\n\n\nTransaction trace:\nconstructor()\nState: x = 0\nproxy()