[fuzzing] Fix msan error in fuzzer (#34783)

test/core/end2end/fuzzers/api_fuzzer.cc

@@ -126,7 +126,7 @@ class FuzzerDNSResolver : public grpc_core::DNSResolver {
       if (name_ == "server") {
         std::vector<grpc_resolved_address> addrs;
         grpc_resolved_address addr;
-        addr.len = 0;
+        memset(&addr, 0, sizeof(addr));
         addrs.push_back(addr);
         on_done_(std::move(addrs));
       } else {

test/core/end2end/fuzzers/api_fuzzer_corpus/5092827311702016

@@ -0,0 +1,35 @@
+actions {
+  create_channel {
+    target: "dns:server"
+    channel_args {
+    }
+  }
+}
+actions {
+  create_call {
+    method {
+      value: "q"
+    }
+    timeout: 31232
+  }
+}
+actions {
+  queue_batch {
+    operations {
+      send_initial_metadata {
+      }
+    }
+  }
+}
+actions {
+  sleep_ms: 262144
+}
+actions {
+}
+actions {
+  watch_connectivity: 0
+}
+config_vars {
+  dns_resolver: "q"
+  experiments: 18446744073709551607
+}