fix corner case in reduce_funcs (#5049)

fixes #5048

lib/compress.js

@@ -10913,9 +10913,10 @@ merge(Compressor.prototype, {
         return self;
     });
 
-    function recursive_ref(compressor, def) {
+    function recursive_ref(compressor, def, fn) {
         var level = 0, node = compressor.self();
         do {
+            if (node === fn) return node;
             if (is_lambda(node) && node.name && node.name.definition() === def) return node;
         } while (node = compressor.parent(level++));
     }
@@ -10951,7 +10952,7 @@ merge(Compressor.prototype, {
                     if ((def.scope !== self.scope.resolve() || def.in_loop)
                         && (!compressor.option("reduce_funcs") || def.escaped.depth == 1 || fixed.inlined)) {
                         single_use = false;
-                    } else if (recursive_ref(compressor, def)) {
+                    } else if (recursive_ref(compressor, def, fixed)) {
                         single_use = false;
                     } else if (fixed.name && fixed.name.definition() !== def) {
                         single_use = false;

test/compress/reduce_vars.js

@@ -7677,3 +7677,22 @@ issue_4949: {
     }
     expect_stdout: "0 1"
 }
+
+issue_5048: {
+    options = {
+        reduce_funcs: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log(function() {
+            var a = function() {
+                return a + 42;
+            };
+        }());
+    }
+    expect: {
+        console.log(function() {}());
+    }
+    expect_stdout: "undefined"
+}