fix issue 829

Needed to make array initialized to null before bpf_probe_read as the
verifier was rejecting the original code. will probably need to fix the
tutorial as well

examples/tracing/nodejs_http_server.py

@@ -23,7 +23,7 @@ bpf_text = """
 #include <uapi/linux/ptrace.h>
 int do_trace(struct pt_regs *ctx) {
     uint64_t addr;
-    char path[128];
+    char path[128]={0};
     bpf_usdt_readarg(6, ctx, &addr);
     bpf_probe_read(&path, sizeof(path), (void *)addr);
     bpf_trace_printk("path:%s\\n", path);