fix corner case in evaluate (#3888)

fixes #3887

lib/compress.js

@@ -3368,7 +3368,7 @@ merge(Compressor.prototype, {
         });
         def(AST_UnaryPostfix, function(compressor, ignore_side_effects, cached, depth) {
             var e = this.expression;
-            if (!(e instanceof AST_SymbolRef)) return this;
+            if (!e.fixed) return this;
             var refs = e.definition().references;
             if (!ignore_side_effects && refs[refs.length - 1] !== e) return this;
             var v = e._eval(compressor, ignore_side_effects, cached, depth + 1);

test/compress/evaluate.js

@@ -2395,3 +2395,26 @@ issue_3882: {
         "NaN",
     ]
 }
+
+issue_3887: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function(b) {
+            try {
+                b-- && console.log("PASS");
+            } catch (a_2) {}
+        })(1);
+    }
+    expect: {
+        (function(b) {
+            try {
+                b-- && console.log("PASS");
+            } catch (a_2) {}
+        })(1);
+    }
+    expect_stdout: "PASS"
+}