nxgdb/mm: warning if corrupted memory node found

If the nodesize is 0, we cannot iterate to next node, siliently return None will cause memleak command to generate false positive report with no warnings.
Add log to indicate such case.

Signed-off-by: xuxingliang <xuxingliang@xiaomi.com>

tools/pynuttx/nxgdb/mm.py

@@ -479,6 +479,7 @@ class MMNode(gdb.Value, p.MMFreeNode):
     @property
     def nextnode(self) -> MMNode:
         if not self.nodesize:
+            gdb.write(f"\n\x1b[31;1m Node corrupted: {self} \x1b[m\n")
             return None
 
         addr = int(self.address) + self.nodesize