IRGenerationContext::internalDispatch(): Fix code generated when the function called via pointer does not return anything

test/libsolidity/semanticTests/functionCall/call_function_returning_nothing_via_pointer.sol

@@ -0,0 +1,19 @@
+contract test {
+    bool public flag = false;
+
+    function f0() public {
+        flag = true;
+    }
+
+    function f() public returns (bool) {
+        function() internal x = f0;
+        x();
+        return flag;
+    }
+}
+
+// ====
+// compileViaYul: also
+// ----
+// f() -> true
+// flag() -> true