Fix crash on J9/Zing: add NULL checks before freeing buffers

Initialize check before freeing _calltrace_buffer and _remote_frame_pool
to prevent crashes on first start when pointers contain uninitialized values.

Also move remote frame pool allocation outside conditional block to ensure
it's reset on every profiler start for clean state.

Author: jbachorik

.claude/settings.local.json

@@ -40,7 +40,8 @@
       "WebFetch(domain:mvnrepository.com)",
       "WebFetch(domain:central.sonatype.com)",
       "Bash(jfr-shell:*)",
-      "Bash(java -cp:*)"
+      "Bash(java -cp:*)",
+      "Bash(git commit:*)"
     ],
     "deny": [],
     "ask": []

ddprof-lib/src/main/cpp/profiler.cpp

@@ -1302,22 +1302,28 @@ Error Profiler::start(Arguments &args, bool reset) {
     size_t nelem = _max_stack_depth + RESERVED_FRAMES;
 
     for (int i = 0; i < CONCURRENCY_LEVEL; i++) {
-      free(_calltrace_buffer[i]);
+      if (_calltrace_buffer[i] != NULL) {
+        free(_calltrace_buffer[i]);
+      }
       _calltrace_buffer[i] = (CallTraceBuffer*)calloc(nelem, sizeof(CallTraceBuffer));
       if (_calltrace_buffer[i] == NULL) {
         _max_stack_depth = 0;
         return Error("Not enough memory to allocate stack trace buffers (try "
                      "smaller jstackdepth)");
       }
+    }
+  }
 
-      // Allocate pre-allocated pool for RemoteFrameInfo (signal-safe storage)
+  // Allocate remote frame pool on every start to ensure clean state
+  for (int i = 0; i < CONCURRENCY_LEVEL; i++) {
+    if (_remote_frame_pool[i] != NULL) {
       free(_remote_frame_pool[i]);
-      _remote_frame_pool[i] = (RemoteFrameInfo*)calloc(MAX_NATIVE_FRAMES, sizeof(RemoteFrameInfo));
-      if (_remote_frame_pool[i] == NULL) {
-        return Error("Not enough memory to allocate remote frame pool");
-      }
-      _remote_frame_count[i] = 0;  // Reset allocation counter
     }
+    _remote_frame_pool[i] = (RemoteFrameInfo*)calloc(MAX_NATIVE_FRAMES, sizeof(RemoteFrameInfo));
+    if (_remote_frame_pool[i] == NULL) {
+      return Error("Not enough memory to allocate remote frame pool");
+    }
+    _remote_frame_count[i] = 0;  // Reset allocation counter
   }
 
   _features = args._features;