Properly resolve virtual modifiers

test/libsolidity/syntaxTests/controlFlow/modifiers/modifier_override.sol

@@ -0,0 +1,17 @@
+contract A {
+	function f() mod internal returns (uint[] storage) {
+	}
+	modifier mod() virtual {
+		revert();
+		_;
+	}
+}
+contract B is A {
+	modifier mod() override { _; }
+	function g() public {
+		f()[0] = 42;
+	}
+}
+// ----
+// Warning 5740: (65-69): Unreachable code.
+// TypeError 3464: (49-63): This variable is of storage pointer type and can be returned without prior assignment, which would lead to undefined behaviour.