fix corner case in pure_getters (#4877)

fixes #4876

lib/compress.js

@@ -3683,10 +3683,13 @@ merge(Compressor.prototype, {
         def(AST_Node, is_strict);
         def(AST_Array, return_false);
         def(AST_Assign, function(compressor) {
-            if (this.operator != "=") return false;
+            var op = this.operator;
-            var rhs = this.right;
-            if (!rhs._dot_throw(compressor)) return false;
             var sym = this.left;
+            var rhs = this.right;
+            if (op != "=") {
+                return lazy_op[op.slice(0, -1)] && (sym._dot_throw(compressor) || rhs._dot_throw(compressor));
+            }
+            if (!rhs._dot_throw(compressor)) return false;
             if (!(sym instanceof AST_SymbolRef)) return true;
             if (rhs instanceof AST_Binary && rhs.operator == "||" && sym.name == rhs.left.name) {
                 return rhs.right._dot_throw(compressor);

test/compress/assignments.js

@@ -672,3 +672,32 @@ issue_4827_3: {
     expect_stdout: "undefined"
     node_version: ">=15"
 }
+
+issue_4876: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        try {
+            var a = null;
+            var b = a &&= 42;
+            b.p;
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            var a = null;
+            var b = a &&= 42;
+            b.p;
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=15"
+}