Tests, Changelog and updated grammar

test/libsolidity/semanticTests/modifiers/function_modifier_empty.sol

@@ -0,0 +1,17 @@
+abstract contract A {
+    function f() public mod returns (bool r) {
+        return true;
+    }
+
+    modifier mod virtual;
+}
+
+
+contract C is A {
+    modifier mod override {
+        if (false) _;
+    }
+}
+
+// ----
+// f() -> false